Added support for DINSM and DINSU bit insertion instructions. Also fixed
errors with bit extraction instructions, added disassembler tests and
adjusted the code to make it more compact.

BUG=
TEST=cctest/test-assembler-mips/Dins
     cctest/test-disasm-mips/Type0

Review-Url: https://codereview.chromium.org/2871663002
Cr-Commit-Position: refs/heads/master@{#45226}