ARM: shmobile: kzm9g: Reference DT implementation

Provide alternate board code for the kzm9g to demonstrate
how DT may be used given the current state of driver
device tree support. This is intended to act as a reference
for mach-shmobile developers.

Some notes:

* Brings up the GIC interrupt handler using device tree
* Brings up the following device using device tree:
  - MMCIF (MMC)
* Does not bring up the INTC interrupt controller at all,
  thus external devices may not be used. In particular,
  the SMSC ethernet device may not be used and thus
  NFS root may not be used.
* Uses existing C code and not device tree to initialise the following,
  which are needed for a working board:
  - SCIF (Serial)
  - CMT (Clock)
  - PFC (GPIO)

To use this alternate board code instead of the normal board code,
CONFIG_MACH_KZM9G_REFERENCE should be selected in the kernel config.
And the sh73a0-kzm9g-reference.dtb flattened device tree blob should be used.

Includes fix by Thierry Reding to no longer use gic_handle_irq()

Includes fixes by Guennadi Liakhovetski for recent pinmux changes.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>