PR28959, obdump doesn't disassemble mftb instruction

Without a -M cpu option given, powerpc objdump defaults currently to
-Mpower10 but -Many is also given.  Commit 1ff6a3b8 regressed
-Many disassembly of instructions that are encoded differently
depending on cpu, such as mftb which has pre- and post-power4
encodings.

	PR 28959
	* ppc-dis.c (lookup_powerpc): Revert 2021-05-28 change.  Instead
	only look at deprecated PPC_OPCODE_RAW bit when -Many.

(cherry picked from commit b508e46b)