wl1271: Move platform device registration from _spi to _main

In order to get the platform device for both SPI and SDIO, move the platform
device registration to wl1271_main.c from wl1271_spi.c.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>