bcmdhd: Rework fw and nvram load

Allow to define fw and nvram paths from BoardConfig parameter without
taking care of weird _b2 extension.

Its used to make a difference between chipset revisions, but since all
golden devices comes with b2, it's not needed.

Also take care of dh-harald commit to fix wifi theter:
https://github.com/dh-harald/android_kernel_samsung_codina/commit/80848dc31c2a42483377388ada1e1c5276a82edb