ARM: shmobile: kzm9g: Support Real Time Clock

KZM-A9-GT board has RTC device r2025d at I2C channel 0
with slave address 0x64.

This patch enables reading and writing hardware real time clock on
KZM-A9-GT board. Interrupt is not yet supported.

How to test this patch using user space command.

Read RTC
 # hwclock -r

Copy system clock to RTC
 # hwclock -w

Shutdown and power off the board, and wait a while, then power on again.
Check RTC still keeps correct date.

Signed-off-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Tested-by: Simon Horman <horms@verge.net.au>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>