egl: move eglCreateDRMImageMESA's malloc later

egl: move eglCreateDRMImageMESA's malloc later

Don't bother allocating any memory until we're finished parsing and
sanitising all the attributes.

As a nice side effect we now consistently set eglError when any of
the attrib/values are not correct.

Strangely enough the spec does not mention _anything_ about what error
should be set where, even if the implementation already sets the odd
one.

Cc: Kristian Høgsberg <krh@bitplanet.net>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>