sunxi: SPL SPI: Add SPI boot support for the Allwinner H616 SoC

sunxi: SPL SPI: Add SPI boot support for the Allwinner H616 SoC

The H616 SoC uses the same SPI IP as the H6, also shares the same clocks
and reset bits.
The only real difference is a slight change in the pin assignment: the
H6 uses PC5, the H616 PC4 instead. This makes for a small change in
our spi0_pinmux_setup() routine.

Apart from that, just extend the H6 #ifdef guards to also cover the H616,
using the shared CONFIG_SUN50I_GEN_H6 symbol.
Also use this symbol for the Kconfig dependency.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Ivan Shishkin <s45rus@gmail.com>