Add sysfs interface to copy VBIOS.

v2: squash in fix for proper vmalloc API (Alex)
Signed-off-by: NAndrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: NLikun Gao <Likun.Gao@amd.com>
Reviewed-by: NHawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>