There are several ways to check out a ATOMBIOS. In previous codes, try
a new way to fetch out vbios/rom, until current vbios/rom is started with
0x55aa, then check if this vbios is ATOMBIOS. Now, try a new way to fetch
out vbios until all flags of ATOMBIOS are verified.
Signed-off-by: Ken Xue <Ken.Xue@amd.com> Reviewed-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>