ARM: exynos: restore mach/regs-clock.h for exynos5

Commit 6e6aac75 "ARM: EXYNOS: Migrate clock support to common
clock framework" from Thomas Abraham removed the Exynos5 specific
register definitions as they were unused at the time, but the
cpufreq driver actually still uses them.

Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: Tomasz Figa <t.figa@samsung.com>
Cc: Thomas Abraham <thomas.abraham@linaro.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>