A dependency on ARCH_SHMOBILE seems to be the best option for sh_keysc:

* For Super H based SoCs: sh_keysc is used on SH_MIGOR, SH_ECOVEC, SH_KFR2R09,
  SH_7722_SOLUTION_ENGINE, and SH_7724_SOLUTION_ENGINE, which depend on
  either CPU_SUBTYPE_SH7722 or CPU_SUBTYPE_SH7724, and both select
  ARCH_SHMOBILE.

* For ARM Based SoCs: Since the removal of legacy (non-multiplatform) support
  this driver has not been used by any Renesas ARM based SoCs. The Renesas
  ARM based SoCs currently select ARCH_SHMOBILE, however, it is planned
  that this will no longer be the case.

This is part of an ongoing process to migrate from ARCH_SHMOBILE to
ARCH_RENESAS the motivation for which being that RENESAS seems to be a more
appropriate name than SHMOBILE for the majority of Renesas ARM based SoCs.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>