lib/nodemask: inline next_node_in() and node_random()

lib/nodemask: inline next_node_in() and node_random()

The functions are pretty thin wrappers around find_bit engine, and
keeping them in c-file prevents compiler from small_const_nbits()
optimization, which must take place for all systems with MAX_NUMNODES
less than BITS_PER_LONG (default is 16 for me).

Moving them to header file doesn't blow up the kernel size:
add/remove: 1/2 grow/shrink: 9/5 up/down: 968/-88 (880)

CC: Andy Shevchenko <[email protected]>
CC: Benjamin Herrenschmidt <[email protected]>
CC: Michael Ellerman <[email protected]>
CC: Paul Mackerras <[email protected]>
CC: Rasmus Villemoes <[email protected]>
CC: Stephen Rothwell <[email protected]>
CC: [email protected]
Signed-off-by: Yury Norov <[email protected]>