sunxi: binman: Move BL31 and SCP firmware addresses to Kconfig

This is easier to read than the #ifdef staircase, provides better
visibility into the memory map (alongside the other Kconfig
definitions), and allows these addresses to be reused from code.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>