sunxi: Move clock_get_pllX / clock_set_pllX protos to mach specific headers

Which pll-s are available depends on the machine type, move the
clock_get_pllX / clock_set_pllX prototypes to the clock_sun?i.h header files
so that we only declare what is actually available. e.g. clock_get_pll5p()
is not available on sun6i / sun8i, and with sun9i we get a completely
different set of plls.

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