[PATCH RFC] frontend.c: Remove the BKL from agp_open

[John Kacur]

@David Airlie. I was looking at the agp driver for removal of the bkl 
lock. From what I could tell, the mutex_lock(&(agp_fe.agp_mutex)) should 
cover what we need. However, I may have easily missed something, and would 
appreciate your review / comments on the patch.