mac80211: brcmfmac: backport firmware loading changes & fix memory bugs

mac80211: brcmfmac: backport firmware loading changes & fix memory bugs

This pick most of brcmfmac changes backported into the master in commits
5932eb690f24 ("mac80211: brcmfmac: backport firmware loading cleanup")
3eab6b8275b2 ("mac80211: brcmfmac: backport NVRAM loading improvements")
529c95cc15dc ("mac80211: brcmfmac: fix use-after-free & possible NULL pointer dereference")

It's more than would be normally backported into a stable branch but it
seems required. Firmware loading cleanups are needed to allow fix memory
bugs in a reliable way. Memory fixes are really important to avoid
corrupting memory and risking a NULL pointer dereference.

Hopefully this stuff has received enough testing in the master.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>