brcmfmac: Create common nvram parsing routines.

New bus layers like pcie require nvram parsing routines which are
the same routines as being used by sdio. Make these routines common
in the new file nvram.c. Update sdio to use these routines and
simplify the nvram upload process. Also add memory validation check
for downloaded firmware and nvram in debug mode.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>