configs: am57xx: change default board name to beagle_x15

beagleboard x15 is the first supported platform variant of am57xx
in AOSP (android open source project) now.

changing board name to stay in consistent with aosp target name.

Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>

configs/am57xx_evm_defconfig

@@ -14,7 +14,7 @@ CONFIG_NR_DRAM_BANKS=2
 CONFIG_SPL_LOAD_FIT=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_USE_BOOTARGS=y
-CONFIG_BOOTARGS="androidboot.serialno=${serial#} console=ttyS2,115200 androidboot.console=ttyS2 androidboot.hardware=am57xevmboard"
+CONFIG_BOOTARGS="androidboot.serialno=${serial#} console=ttyS2,115200 androidboot.console=ttyS2 androidboot.hardware=beagle_x15board"
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 # CONFIG_MISC_INIT_R is not set

configs/am57xx_hs_evm_defconfig

@@ -20,7 +20,7 @@ CONFIG_SPL_LOAD_FIT=y
 CONFIG_SPL_FIT_IMAGE_POST_PROCESS=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_USE_BOOTARGS=y
-CONFIG_BOOTARGS="androidboot.serialno=${serial#} console=ttyS2,115200 androidboot.console=ttyS2 androidboot.hardware=am57xevmboard"
+CONFIG_BOOTARGS="androidboot.serialno=${serial#} console=ttyS2,115200 androidboot.console=ttyS2 androidboot.hardware=beagle_x15board"
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 # CONFIG_MISC_INIT_R is not set