ARM: shmobile: Enable R-Mobile reset driver in multiplatform defconfig

This is used on R-Mobile APE6 (r8a73a4), R-Mobile A1 (r8a7740), and
SH-Mobile AG5 (sh73a0).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>