gpio-rcar: Add support for IRQ_TYPE_EDGE_BOTH

As hardware support for this feature is not universal for all SoCs a flag,
has_both_edge_trigger, has been added to the platform data of the driver to
allow this feature to be enabled.

The motivation for this is to allow use of the gpio-keys driver on the
lager board which is based on the r8a7790 SoC. The V2 of this patch has been
fully exercised using that driver on that board.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>