Add R8A7794 GPIO DT support

Hello.

Here's the set of 2 patches against Simon Horman's 'renesas.git' repo,
'renesas-devel-20150807-v4.2-rc5' tag. Here we add the GPIO device tree support for the R8A7794 SoC.

[1/2] ARM: shmobile: r8a7794: add GPIO clocks
[2/2] ARM: shmobile: r8a7794: add GPIO DT support

WBR, Sergei