lib: move find_last_bit to lib/find_next_bit.c

lib: move find_last_bit to lib/find_next_bit.c

Currently all 'find_*_bit' family is located in lib/find_next_bit.c,
except 'find_last_bit', which is in lib/find_last_bit.c. It seems,
there's no major benefit to have it separated.

Signed-off-by: Yury Norov <[email protected]>
Reviewed-by: Rasmus Villemoes <[email protected]>
Reviewed-by: George Spelvin <[email protected]>
Cc: Alexey Klimov <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Hannes Frederic Sowa <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Mark Salter <[email protected]>
Cc: AKASHI Takahiro <[email protected]>
Cc: Thomas Graf <[email protected]>
Cc: Valentin Rothberg <[email protected]>
Cc: Chris Wilson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>