MIPS/opcodes: Correctly combine ASE flags for ASE_MIPS16E2_MT calculation

MIPS/opcodes: Correctly combine ASE flags for ASE_MIPS16E2_MT calculation

Correct a commit 25499ac7ee92 ("MIPS16e2: Add MIPS16e2 ASE support")
disassembler bug with the handling of the ASE_MIPS16E2_MT combination
ASE flag, where the calculation uses MIPS ABI Flags directly rather than
calculated internal ASE flags.  Consequently code does not correctly set
the ASE_MIPS16E2_MT flag when the MIPS16e2 ASE flag and the MT ASE flag
come from different sources, i.e. one from the BFD chosen and the other
one from MIPS ABI Flags.

Fix this by using internal ASE_MT and ASE_MIPS16E2 flags in a separate
subsequent step, factored out to a dedicated function for use with
future combination ASE flags.  Adjust the `mips16e2@mips16e2-mt-sub.d'
test case accordingly, where the MT flag comes from the BFD selected for
the disassembler and the MIPS16e2 flag comes from the ELF binary itself.

	opcodes/
	* mips-dis.c (mips_calculate_combination_ases): New function.
	(mips_convert_abiflags_ases): Factor out ASE_MIPS16E2_MT
	calculation to the new function.
	(set_default_mips_dis_options): Call the new function.

	gas/
	* testsuite/gas/mips/mips16e2@mips16e2-mt-sub.d: Adjust for the
	ASE_MIPS16E2_MT flag disassembler fix.
	* testsuite/gas/mips/mips16e2-interaptiv-mr2@mips16e2-mt-sub.d:
	Likewise.