drm/vc4: Use drm_print_regset32() for our debug register dumping.

This removes a bunch of duplicated boilerplate for the debugfs vs
runtime printk debug dumping.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190220210343.28157-2-eric@anholt.net
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>