Hi,

This patch adds a framework to OBJDUMP to support MVE instructions.

Since MVE and NEON share some encoding space, but may need a slightly 
different decoding, we decided to split up instruction decoding based on 
whether '-marmv8.1-m.main' has been passed to OBJDUMP.  The new function 
'is_mve_architecture' will check this and direct 'print_insn_thumb32' to 
either use 'print_insn_neon' or 'print_insn_mve'.

This framework also includes helper functions to determine encoding 
conflicts, undefined encodings and unpredictable encodings.  These are 
further implemented for each relevant instruction in subsequent patches.

By encoding conflicts we refer to encodings where two different 
instructions have overlapping base opcodes, but can be distinguished 
based on specific operand values.  In the ISA specification such 
'conflicts' can be identified by looking for clauses that redirect you 
to 'Related Encodings' or specific instructions.  The VMLALDAV 
instruction is an example of the latter, where if RdaHi (bits 20-22) has 
value 7, then the encoding is actually to be decoded as the VMLADAV 
instruction.

This patch also sets force_thumb when passing '-marmv8.1-m.main' to 
objdump. This makes it unnecessary to use '-M force-thumb' when 
disassembling for non-elf targets.

opcodes/ChangeLog:

2019-05-01  Andre Vieira  <andre.simoesdiasvieira@arm.com>
             Michael Collison <michael.collison@arm.com>

	* arm-dis.c (enum mve_instructions): New enum.
	(enum mve_unpredictable): Likewise.
	(enum mve_undefined): Likewise.
	(struct mopcode32): New struct.
	(is_mve_okay_in_it): New function.
	(is_mve_architecture): Likewise.
	(arm_decode_field): Likewise.
	(arm_decode_field_multiple): Likewise.
	(is_mve_encoding_conflict): Likewise.
	(is_mve_undefined): Likewise.
	(is_mve_unpredictable): Likewise.
	(print_mve_undefined): Likewise.
	(print_mve_unpredictable): Likewise.
	(print_insn_coprocessor_1): Use arm_decode_field_multiple.
	(print_insn_mve): New function.
	(print_insn_thumb32): Handle MVE architecture.
         (select_arm_features): Force thumb for Armv8.1-m Mainline.