loader: Create new gfx table

Create a new gfx global table. Put into it all the graphics bindings
that we have in loader today. For now, have compatability binding for
loader. Remove them from loader.

Sponsored by: Netflix
Reviewed by: kevans, jhb
Differential Revision: https://reviews.freebsd.org/D43902

(cherry picked from commit 9b16231032ddb40be282d76ec0d82b3a0ec96d60)