spl: rename config item SPL_ATF_SUPPORT to SPL_ATF

Having CONFIG_SPL_ATF seems more natural.
Rename it, while it it is easy and there's few boards that use it
(only RK3399 and RK3368 boards).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/spl/Kconfig

@@ -702,7 +702,7 @@ config SPL_YMODEM_SUPPORT
 	  means of transmitting U-Boot over a serial line for using in SPL,
 	  with a checksum to ensure correctness.
 
-config SPL_ATF_SUPPORT
+config SPL_ATF
 	bool "Support ARM Trusted Firmware"
 	depends on ARM64
 	help

common/spl/Makefile

@@ -22,7 +22,7 @@ endif
 obj-$(CONFIG_$(SPL_TPL_)UBI) += spl_ubi.o
 obj-$(CONFIG_$(SPL_TPL_)NET_SUPPORT) += spl_net.o
 obj-$(CONFIG_$(SPL_TPL_)MMC_SUPPORT) += spl_mmc.o
-obj-$(CONFIG_$(SPL_TPL_)ATF_SUPPORT) += spl_atf.o
+obj-$(CONFIG_$(SPL_TPL_)ATF) += spl_atf.o
 obj-$(CONFIG_$(SPL_TPL_)USB_SUPPORT) += spl_usb.o
 obj-$(CONFIG_$(SPL_TPL_)FAT_SUPPORT) += spl_fat.o
 obj-$(CONFIG_$(SPL_TPL_)EXT_SUPPORT) += spl_ext.o