[why]
Some parts are consuming dangerously close to maximum number of states
supported when updating the BB (i.e. 8).

[how]
Change maximum stages from 9 to 20.
Reviewed-by: NAlvin Lee <Alvin.Lee2@amd.com>
Acked-by: NHamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: NJun Lei <jun.lei@amd.com>
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>