ARM: shmobile: r8a7779: Initial multiplatform support

Add Marzen and r8a7779 to CONFIG_SHMOBILE_MULTI. At this
point CCF is not yet supported so you cannot run this code
yet. For CCF support to happen several different components
are needed, and this is one simple portion that moves us
forward. Other patches need to build on top of this one.

Marzen board support exists in 3 flavours:
1) SHMOBILE_MULTI, MACH_MARZEN - board-marzen-reference.c (CCF + DT)
2) SHMOBILE, MACH_MARZEN_REFERENCE - board-marzen-reference.c (DT)
3) SHMOBILE, MACH_MARZEN - board-marzen.c (legacy C code)

When CCF is done then 2) will be removed. When 1) includes same features
as 3) then 3) will be removed.

Based on work for the Koelsch and r8a7791 by Magnus Damm.

Cc: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>