drm/imagination: Numerous documentation fixes.

Some reported by Stephen Rothwell. The rest were found by running the
kernel-doc build script.
Some indentation fixes.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311241526.Y2WZeUau-lkp@intel.com/


Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231128173507.95119-1-donald.robson@imgtec.com