[ARCH] Introduce generic arch dependent clocking interface

This patch adds arch/include/arch_clk.h which is an interface to arch dependent clocking APIs

The arch_clk.h is similar linux/clk.h which enables us to have a linux compatible linux/clk.h

The clocking code is a crucial part of SOC programming we would like to have minimum efforts in porting clocking related code from linux to xvisor.

Due to this patch, we will be soon deprecating vmm_devdrv_clock_xxx() APIs and also remove struct vmm_devclk.

Signed-off-by: Anup Patel <anup@brainfault.org>
[DRIVERS] Exynos4: temporary fix for Exynos RTC driver.

A better long trem solution will be added when the Exynos clocking Framework is merged in.

Signed-off-by: Anup Patel <anup@brainfault.org>
Merge remote-tracking branch 'upstream/master' into dev_exynos4

Conflicts:
	arch/arm/board/common/include/versatile/clock.h
	arch/arm/board/common/versatile/clock.c
	drivers/rtc/rtc-s3c.c

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DRIVERS] Exynos4: improve linux port related to clock.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DRIVERS] Exynos4: Use clk for serial clock rate if available.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[ARM] Exynos4: move to a per PTF clock definition.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>