staging/bcm: move IOCTL_BCM_NVM_[READ|WRITE] cases out to their own function.

bcm_char_ioctl is one of the longest non-generated functions in the kernel,
at 1906 lines.  Splitting it up into multiple functions should simplify
this a lot.
Signed-off-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>