am33xx: Finish migration of CONFIG_AM33XX/AM43XX

Almost all users of CONFIG_AM33XX/AM43XX have been migrated.  Finish
moving the last few over to Kconfig, and put all of the boards under the
appropriate Kconfig chocie now.  This board choice is non-optional, so
remove that keyword on am33xx.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/thuban_defconfig b/configs/thuban_defconfig
index 914f70f..4c07de7 100644
--- a/configs/thuban_defconfig
+++ b/configs/thuban_defconfig
@@ -4,8 +4,9 @@
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
-CONFIG_TARGET_THUBAN=y
+CONFIG_AM33XX=y
 CONFIG_SYS_MPUCLK=300
+CONFIG_TARGET_THUBAN=y
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y