ARM: shmobile: Introduce ARCH_RENESAS

The purpose of this patch is to start the process of replacing both
ARCH_SHMOBILE and ARCH_SHMOBILE_MULTI with ARCH_RENESAS.

RENESAS seems to be a more appropriate name than SHMOBILE for the majority
of Renesas 32-bit ARM based SoCs. The name is conveniently also (newer)
ARM64 based SoCs.

This patches only addresses 32-bit ARM based SoCs.  Proposed support for
the ARM64 based r8a7795 SoC already uses ARCH_RENESAS which selects
ARCH_SHMOBILE.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>