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/am3517_evm_defconfig b/configs/am3517_evm_defconfig
index 54b857c..04bade9 100644
--- a/configs/am3517_evm_defconfig
+++ b/configs/am3517_evm_defconfig
@@ -1,7 +1,8 @@
 CONFIG_ARM=y
 # CONFIG_SYS_THUMB_BUILD is not set
-CONFIG_OMAP34XX=y
+CONFIG_ARCH_OMAP2PLUS=y
 # CONFIG_SPL_GPIO_SUPPORT is not set
+CONFIG_OMAP34XX=y
 CONFIG_TARGET_AM3517_EVM=y
 CONFIG_SYS_EXTRA_OPTIONS="NAND"
 CONFIG_BOOTDELAY=10