drm: Try loading builtin EDIDs first

If the firmware is not builtin and userspace is not yet running, we can
stall the boot process for a minute whilst the firmware loader times
out. This is contrary to expectations of providing a builtin EDID!

In the process, we can rearrange the code to make the error handling
more resilient and prevent gcc warning about unitialised variables along
the error paths.

v2: Load builtins first, fix gcc second (Jani) and cosmetics (Ville).
v3: Verify that we do not read beyond the end of the fwdata (Ville)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>