wl12xx: 1281/1283 support - use dynamic memory for the RX/TX pools

Separate the memory configuration to chip-specific structures and
implement dynamic memory for wl128x.

This feature allows us to move TX memory blocks to the RX pool when
the RX path is overloaded.

Thanks for Arik Nemtsov <arik@wizery.com> for helping simplify the
wl1271_fw_status() code.

[Rewrote the commit subject and message for clarity; improved some
comments and changed "spare" to "padding" for consistency; added a
FIXME for the AP memory configuration -- Luca]

Signed-off-by: Shahar Levi <shahar_levi@ti.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>