ARM: shmobile: Remove non-multiplatform Koelsch reference support
Now that r8a7791 has CCF support remove the legacy Koelsch reference
Kconfig bits CONFIG_MACH_KOELSCH_REFERENCE for the non-multiplatform
case.
Starting from this commit Koelsch board support is always enabled via
CONFIG_MACH_KOELSCH, and CONFIG_ARCH_MULTIPLATFORM is used to select
between board-koelsch.c and board-koelsch-reference.c
The file board-koelsch-reference.c can no longer be used together with
the legacy sh-clk clock framework, instead CCF is used.