MFC _umtx_op: documentation and libsysdecode/kdump/truss decoding (32-bit)

e04a83a3: _umtx_op(2): document recent addition of 32bit compat flags

This was part of D27325.

3b27074b: libsysdecode: decode _UMTX_OP flags

Assume that UMTX_OP with a double underbar following is a flag, while any
underbar+alphanumeric combination immeiately following is an op.

This was a part of D27325.

c2679dd7: kdump/truss: decode new _umtx_op flags

In both cases, print the flag bits first followed by the command.

Output now looks something like this:

(ktrace)
_umtx_op(0x8605f7008,0xf<UMTX_OP_WAIT_UINT_PRIVATE>,0,0,0)
_umtx_op(0x9fffdce8,0x80000003<UMTX_OP__32BIT|UMTX_OP_WAKE>,0x1,0,0)

(truss)
_umtx_op(0x7fffffffda50,UMTX_OP_WAKE,0x1,0x0,0x0) = 0 (0x0)
_umtx_op(0x9fffdd08,UMTX_OP__32BIT|UMTX_OP_WAKE,0x1,0x0,0x0) = 0 (0x0)

(cherry picked from commit e04a83a3e1b40fc7c41b5938d2e432ba01facd74)
(cherry picked from commit 3b27074b252cae3c7aee8f05f0c968dd26fa055b)
(cherry picked from commit c2679dd779bb75f51682cde5eb55a291b72d7900)