find: support -perm /BITS. Closes 7340

function                                             old     new   delta
parse_params                                        1487    1497     +10
func_perm                                             57      61      +4
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(add/remove: 0/0 grow/shrink: 2/0 up/down: 14/0)               Total: 14 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>