wlcore/wl12xx: calibrator fem detect implementation

this completes the calibrator based fem detect logic in driver:
driver starts (by calibrator) in plt_mode PLT_FEM_DETECT
wlcore inits and starts plt on wl12xx
wl12xx fetches fem number from firmware and stores it in wl->fem_manuf
wl12xx immediatly returns (doesn't start radio, etc...)
wlcore returns the fem_manuf to calibrator using WL1271_TM_ATTR_DATA
plt_mode is stopped

Signed-off-by: Yair Shapira <yair.shapira@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>