ARM: shmobile: r8a7790: add QSPI support

Adds support for QSPI on the r8a7790.

Signed-off-by: Hiep Cao Minh <cm-hiep@jinso.co.jp>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>