sun6i: Add clock functions needed for SPL / DRAM init

sun6i: Add clock functions needed for SPL / DRAM init

Add clock_init_safe and clockset_pll5 functions, as these are needed for
SPL support resp. DRAM init (which is needed for SPL too).

Also add some extra clock register constant defines.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>