ARM: shmobile: Remove MEMORY_START/SIZE

Remove CONFIG_MEMORY_START and CONFIG_MEMORY_SIZE from mach-shmobile.

Boards should use DT to specify their memory setup. Boards that still
not support DT may pass ATAGS with memory information from the boot
loader. If those ATAGS turn out to be incorrect then appended DTB with
memory information should be used as a workaround.

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