wl12xx: Clean up the block size alignment code

Simplify and clean up the block size alignment code:
1. Set the block size according to the padding field type, as it cannot
   exceed the maximum value this field can hold.
2. Move the alignment code into a function instead of duplicating it in
   multiple places.
3. In the current implementation, the block_size member can be
   misleading because a zero value actually means that there's no need to
   align. Declare a block size alignment quirk instead.

Signed-off-by: Ido Yariv <ido@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>