ARM: shmobile: r8a7779: Add clocks

Declare all core and MSTP clocks currently used by r8a7779-based boards.

Based on work by Laurent Pinchart for the r8a7790 and r8a7791 SoCs.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>