ARM: integrator: move board select into mach-integrator/Kconfig

The board/SoC select menu in arch/arm/Kconfig is still cluttered.
Add ARCH_INTEGRATOR into arch/arm/Kconfig and move the board select
under arch/arm/mach-integrator.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
diff --git a/configs/integratorap_cm926ejs_defconfig b/configs/integratorap_cm926ejs_defconfig
index 308a1e6..af4cfa5 100644
--- a/configs/integratorap_cm926ejs_defconfig
+++ b/configs/integratorap_cm926ejs_defconfig
@@ -1,3 +1,4 @@
 CONFIG_SYS_EXTRA_OPTIONS="CM926EJ_S"
 CONFIG_ARM=y
+CONFIG_ARCH_INTEGRATOR=y
 CONFIG_TARGET_INTEGRATORAP_CM926EJS=y