ARM: shmobile: genmai: Rename ARCH_SHMOBILE to ARCH_SHMOBILE_LEGACY

The ARCH_SHMOBILE configuration option has been renamed to
ARCH_SHMOBILE_LEGACY. Update the defconfig accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Magnus Damm <damm@opensource.se>
[ horms+renesas@verge.net.au: Removed non-genmai changes which
  have been squashed into "ARM: Rename ARCH_SHMOBILE to ARCH_SHMOBILE_LEGACY". ]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>