drm/sun4i: Update Kconfig defaults and descriptions

Allwinner display drivers are split roughly into two generations. The
first generation was found on early 32-bit ARM SoCs and contains DE1.0
and a custom HDMI controller. Clarify that these options only apply to
a specific list of SoCs, and limit selecting them to 32-bit ARM, to
avoid confusion.

The second generation, found in A83T and newer SoCs (both 32-bit and
64-bit), contains a DE2.0 and a DesignWare HDMI controller. Since this
is the most widely-used generation, enable it by default. The previous
default condition (MACH_SUN8I) was limited to 32-bit SoCs. Also enable
the DSI controller by default, which is found on 64-bit SoCs as well.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220702193250.52959-1-samuel@sholland.org