MSP430: Add defaulting to the insn length attribute

MSP430: Add defaulting to the insn length attribute

The length of MSP430 instructions is mostly just a function of the type
and number of operands. Setting the "type" attribute on all insns
describes the number of operands, and the position of the source and
destination operands.

In most cases, defaulting in the "length" and "extension" attribute
definitions can then be used to calculate the total length of the
instruction by using the value of the "type" attribute to examine the
operands.

gcc/ChangeLog:

	* config/msp430/msp430-protos.h (msp430x_extendhisi): Return int
	instead of char *.
	(msp430_output_asm_shift_insns): Likewise.
	Add new return_length argument.
	(msp430x_insn_required): Add prototype.
	* config/msp430/msp430.c (msp430_output_asm_shift_insns): Return the
	total length, in bytes, of the emitted instructions.
	(msp430x_insn_required): New function.
	(msp430x_extendhisi): Return the total length, in bytes, of the
	emitted instructions.
	* config/msp430/msp430.h (ADJUST_INSN_LENGTH): Define.
	* config/msp430/msp430.md: New define_attr "type".
	New define_attr "extension".
	New define_attr "length_multiplier".
	New define_attr "extra_length".
	Rewrite define_attr "length".
	Set type, extension, length, length_multiplier or extra_length insn
	attributes on all insns, as appropriate.
	(andneghi3): Rewrite using constraints instead of C code to decide
	output insns.
	* config/msp430/predicates.md (msp430_cheap_operand): New predicate.
	(msp430_high_memory_operand): New predicate.