MHU doorbell driver requires arm platform specific
macro "PLAT_CSS_MHU_BASE".
Rename it to "PLAT_MHUV2_BASE", so that platforms other than arm
can use generic MHU doorbell driver.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>

Replace all usage of 'sgiclark' with 'rdn1e1edge' and 'sgiclarka' with
'rdn1edge' as per the updated product names.

Change-Id: Idbc157c73477ec32f507ba2d4a4e907d8813374c
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>