ARM: omap2+: rename config to ARCH_OMAP2PLUS and consolidate Kconfig

In Linux, CONFIG_ARCH_OMAP2PLUS is used for OMAP2 or later SoCs.
Rename CONFIG_ARCH_OMAP2 to CONFIG_ARCH_OMAP2PLUS to follow this
naming.

Move the OMAP2+ board/SoC choice down to mach-omap2/Kconfig to slim
down the arch/arm/Kconfig level.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am43xx_evm_usbhost_boot_defconfig b/configs/am43xx_evm_usbhost_boot_defconfig
index a938350..50cca20 100644
--- a/configs/am43xx_evm_usbhost_boot_defconfig
+++ b/configs/am43xx_evm_usbhost_boot_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
-CONFIG_AM43XX=y
+CONFIG_ARCH_OMAP2PLUS=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
+CONFIG_AM43XX=y
 CONFIG_TARGET_AM43XX_EVM=y
 CONFIG_ISW_ENTRY_ADDR=0x40300350
 CONFIG_SPL_STACK_R_ADDR=0x82000000