sunxi: Introduce a hidden SUNXI_GEN_SUNxI Kconfig bool

sunxi: Introduce a hidden SUNXI_GEN_SUNxI Kconfig bool

sun6i and newer (derived) SoCs such as the sun8i-a23, sun8i-a33 and sun9i
have a various things in common, like having separate ahb reset control
registers, the SID living inside the pmic, custom pmic busses, new style
watchdog, etc.

This commit introduces a new hidden SUNXI_GEN_SUN6I Kconfig bool which can be
used to check for these features avoiding the need for an ever growing list
of "#if defined CONFIG_MACH_SUN?I" conditionals as we add support for more
"new style" sunxi SoCs.

Note that this commit changes the behavior of the gmac and hdmi code for
sun8i and the upcoming sun9i devices. This does not matter as sun8i does
not have gmac nor hdmi, and sun9i has new hardware-blocks for these so
the old code will not work there.

Also this is intentional as if a sun8i / sun9i variant which does use the
old hwblocks shows up then the GEN_SUN6I code paths will be the right ones
to use.

For completeness this also adds a SUNXI_GEN_SUN4I bool for A10/A13/A20.

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