ARM: SAMSUNG: local regs-srom header in mach-exynos

This patch moves regs-srom header file into mach-exynos.
Because it is not used for others except mach-exynos.

Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>