[Mips] Add support to match more patterns for DEXT and CINS

This patch adds support for recognizing more patterns to match to DEXT and
CINS instructions.
It finds cases where multiple instructions could be replaced with a single
DEXT or CINS instruction.

For example, for the following:

define i64 @dext_and32(i64 zeroext %a) {
entry:

 %and = and i64 %a, 4294967295
 ret i64 %and
}

instead of generating:

 0000000000000088 <dext_and32>:

 88:   64010001        daddiu  at,zero,1
 8c:   0001083c        dsll32  at,at,0x0
 90:   6421ffff        daddiu  at,at,-1
 94:   03e00008        jr      ra
 98:   00811024        and     v0,a0,at
 9c:   00000000        nop

the following gets generated:

 0000000000000068 <dext_and32>:

 68:   03e00008        jr      ra
 6c:   7c82f803        dext    v0,a0,0x0,0x20

Cases that are covered:

DEXT:

 1. and $src, mask where mask > 0xffff
 2. zext $src zero extend from i32 to i64

CINS:

 1. and (shl $src, pos), mask
 2. shl (and $src, mask), pos
 3. zext (shl $src, pos) zero extend from i32 to i64

Patch by Violeta Vukobrat.

Differential Revision: https://reviews.llvm.org/D30464

llvm-svn: 297832