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/integratorcp_cm946es_defconfig b/configs/integratorcp_cm946es_defconfig
index 2e67dbc..dcd034d 100644
--- a/configs/integratorcp_cm946es_defconfig
+++ b/configs/integratorcp_cm946es_defconfig
@@ -1,3 +1,4 @@
 CONFIG_SYS_EXTRA_OPTIONS="CM946ES"
 CONFIG_ARM=y
+CONFIG_ARCH_INTEGRATOR=y
 CONFIG_TARGET_INTEGRATORCP_CM946ES=y