ARM: shmobile: Enable r8a7794 SoC in shmobile_defconfig

Support for the r8a7794 was recently added.
Enable it in the shmobile_defconfig to increase build coverage.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/configs/shmobile_defconfig

@@ -16,6 +16,7 @@ CONFIG_ARCH_R8A7740=y
 CONFIG_ARCH_R8A7779=y
 CONFIG_ARCH_R8A7790=y
 CONFIG_ARCH_R8A7791=y
+CONFIG_ARCH_R8A7794=y
 CONFIG_MACH_KOELSCH=y
 CONFIG_MACH_LAGER=y
 CONFIG_MACH_MARZEN=y