arm: Move sp810.h to include/linux/amba/

Since it is now used by code under drivers/clk/ it makes sense for this
file to be in a more generic location. This is required for building
vexpress support on arm64.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Pawel Moll <pawel.moll@arm.com>
Cc: Shiraz Hashim <shiraz.hashim@st.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>