pfmask: Limit the preferred mask to the vendor specific flags
pfmask: Limit the preferred mask to the vendor specific flags

In ndisasm, the priority follows the order of instructions in insns.dat.
Other iflags could affect this mechanism when a proper instruction form
had a higher iflag bit set.
The preferred mask bits are now limited to vendor flags (Cyrix and AMD)
and other flags do not affect disassembler any more.

Signed-off-by: Jin Kyu Song <636a629b48a15ad840070a3dd8c6df980563dd68@intel.com>

projedi/nasm,projedi/nasm,techkey/nasm,techkey/nasm,techkey/nasm,projedi/nasm,techkey/nasm,projedi/nasm,techkey/nasm,projedi/nasm