ARM: 7257/1: EXYNOS: introduce arch/arm/mach-exynos/common.[ch]

This patch introduces common.[ch] which are used only in the
arch/arm/mach-exynos/ directory. The common.c file merges
the cpu.c, init.c, irq-combiner.c and irq-eint.c files which
are used commonly on EXYNOS SoCs and the common.h file replaces
with plat/exynos4.h file.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>