hw/display/pl110: Pull included-once parts of template header into pl110.c

hw/display/pl110: Pull included-once parts of template header into pl110.c

The pl110_template.h header has a doubly-nested multiple-include pattern:
 * pl110.c includes it once for each host bit depth (now always 32)
 * every time it is included, it includes itself 6 times, to account
   for multiple guest device pixel and byte orders

Now we only have to deal with 32-bit host bit depths, we can move the
code corresponding to the outer layer of this double-nesting to be
directly in pl110.c and reduce the template header to a single layer
of nesting.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20210211141515.8755-3-peter.maydell@linaro.org