From: Rusty Russell <rusty@rustcorp.com.au>

clear_bit(n, addr) clears the nth bit.
test_and_clear_bit(n, addr) clears the nth bit.
cpu_clear(n, cpumask) clears the nth bit (vs. cpus_clear()).
bitmap_clear(bitmap, n) clears out all the bits up to n.

Moreover, there's a CLEAR_BITMAP() in linux/types.h which bitmap_clear() is
a wrapper for.

Rename bitmap_clear to bitmap_zero, which is harder to confuse (yes, it bit
me), and make everyone use it.