ARM: shmobile: r8a7779: Generic SMP ops

Add a r8a7779-specific SMP operation pointer to support
all 4 CPU cores through SMP on r8a7779 without C board code.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>