sandbox: set sandbox's vendor to null

Because sandbox is not a real hardware, setting vendor=sandbox is
almost meaningless.

This commit sets sandbox's vendor field to '-'.

It is a good thing that it decreases one level directory hierarchy.
The files board/sandbox/sandbox/* have been moved to board/sandbox/*.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

boards.cfg

@@ -1183,7 +1183,7 @@ Active  powerpc     ppc4xx         -           xilinx          ppc405-generic
 Active  powerpc     ppc4xx         -           xilinx          ppc405-generic      xilinx-ppc405-generic_flash           xilinx-ppc405-generic:SYS_TEXT_BASE=0xF7F60000,RESET_VECTOR_ADDRESS=0xF7FFFFFC                                                    Ricardo Ribalda <ricardo.ribalda@uam.es>
 Active  powerpc     ppc4xx         -           xilinx          ppc440-generic      xilinx-ppc440-generic                 xilinx-ppc440-generic:SYS_TEXT_BASE=0x04000000,RESET_VECTOR_ADDRESS=0x04100000,BOOT_FROM_XMD=1                                    Ricardo Ribalda <ricardo.ribalda@uam.es>
 Active  powerpc     ppc4xx         -           xilinx          ppc440-generic      xilinx-ppc440-generic_flash           xilinx-ppc440-generic:SYS_TEXT_BASE=0xF7F60000,RESET_VECTOR_ADDRESS=0xF7FFFFFC                                                    Ricardo Ribalda <ricardo.ribalda@uam.es>
-Active  sandbox     sandbox        -           sandbox         sandbox             sandbox                               -                                                                                                                                 Simon Glass <sjg@chromium.org>
+Active  sandbox     sandbox        -           -               sandbox             sandbox                               -                                                                                                                                 Simon Glass <sjg@chromium.org>
 Active  sh          sh2            -           renesas         rsk7203             rsk7203                               -                                                                                                                                 Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>:Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
 Active  sh          sh2            -           renesas         rsk7264             rsk7264                               -                                                                                                                                 Phil Edworthy <phil.edworthy@renesas.com>
 Active  sh          sh2            -           renesas         rsk7269             rsk7269                               -                                                                                                                                 -