wl1271: Implement chipset boot retry

The wl1271 has a hardware bug which causes it to randomly (very infrequently)
to fail powering up properly. This patch implements retry for the chipset boot
sequence, to work around the hardware problem.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>