ARM: uniphier: allow to enable multiple SoCs

Before this commit, the Kconfig menu in mach-uniphier only allowed us
to choose one SoC to be compiled.  Each SoC has its own defconfig file
for the build-test coverage.  Consequently, some defconfig files are
duplicated with only the difference in CONFIG_DEFAULT_DEVICE_TREE and
CONFIG_{SOC_NAME}=y.

Now, most of board-specific parameters have been moved to device trees,
so it makes sense to include init code of multiple SoCs into a single
image as long as the SoCs have similar architecture.  In fact, some
SoCs of UniPhier family are very similar:
 - PH1-LD4 and PH1-sLD8
 - PH1-LD6b and ProXstream2 (will be added in the upcoming commit)

This commit will be helpful to merge some defconfig files for better
maintainability.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/ph1_pro4_defconfig b/configs/ph1_pro4_defconfig
index 139767a..aaf1f46 100644
--- a/configs/ph1_pro4_defconfig
+++ b/configs/ph1_pro4_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_UNIPHIER=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
+CONFIG_ARCH_UNIPHIER_PH1_PRO4=y
 CONFIG_MICRO_SUPPORT_CARD=y
 CONFIG_SYS_TEXT_BASE=0x84000000
 CONFIG_DEFAULT_DEVICE_TREE="uniphier-ph1-pro4-ref"