clocksource/drivers/gemini: Add driver for the Cortina Gemini

This is a rewrite of the Gemini timer
driver in arch/arm/mach-gemini/timer.c trying to do everything
the device tree way:

- Make every IO-access relative to a base address and dynamic
  so we can do a dynamic ioremap and get going.
- Do not poke around directly in the global syscon registers,
  access them using the syscon regmap style design pattern for
  the one register we need to check.
- Find register range and interrupt from the device tree.

Cc: Janos Laube <janos.dev@gmail.com>
Cc: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Cc: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Makefile

@@ -16,6 +16,7 @@ obj-$(CONFIG_CLKSRC_MMIO)	+= mmio.o
 obj-$(CONFIG_DIGICOLOR_TIMER)	+= timer-digicolor.o
 obj-$(CONFIG_DW_APB_TIMER)	+= dw_apb_timer.o
 obj-$(CONFIG_DW_APB_TIMER_OF)	+= dw_apb_timer_of.o
+obj-$(CONFIG_GEMINI_TIMER)	+= timer-gemini.o
 obj-$(CONFIG_ROCKCHIP_TIMER)      += rockchip_timer.o
 obj-$(CONFIG_CLKSRC_NOMADIK_MTU)	+= nomadik-mtu.o
 obj-$(CONFIG_CLKSRC_DBX500_PRCMU)	+= clksrc-dbx500-prcmu.o