macintosh: Remove BKL from nvram driver

Drop the bkl from nvram_llseek() as it obviously protects nothing. The
file offset is safe in essence.

The ioctl can be converted to unlocked_ioctl because it just calls
pmac_get_partition() which reads a value from an array which was
initialized at early boot time. No need for serialization.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>