xtensa: Optimize bitwise AND operation with some specific forms of constants

xtensa: Optimize bitwise AND operation with some specific forms of constants

This patch offers several insn-and-split patterns for bitwise AND with
register and constant that can be represented as:

i.   1's least significant N bits and the others 0's (17 <= N <= 31)
ii.  1's most significant N bits and the others 0's (12 <= N <= 31)
iii. M 1's sequence of bits and trailing N 0's bits, that cannot fit into a
	"MOVI Ax, simm12" instruction (1 <= M <= 16, 1 <= N <= 30)

And also offers shortcuts for conditional branch if each of the abovementioned
operations is (not) equal to zero.

gcc/ChangeLog:

	* config/xtensa/predicates.md (shifted_mask_operand):
	New predicate.
	* config/xtensa/xtensa.md (*andsi3_const_pow2_minus_one):
	New insn-and-split pattern.
	(*andsi3_const_negative_pow2, *andsi3_const_shifted_mask,
	*masktrue_const_pow2_minus_one, *masktrue_const_negative_pow2,
	*masktrue_const_shifted_mask): Ditto.