[GlobalISel][InstructionSelect] MatchTable second level grouping, perf patch 5

This patch continues a series of patches started by r332907 (reapplied
as r332917)

In this commit we start grouping rules with common first condition on
the second level of the table.

This is expected to decrease time GlobalISel spends in its
InstructionSelect pass by roughly 13% for an -O0 build as measured on
sqlite3-amalgamation (http://sqlite.org/download.html) targeting
AArch64.

Reviewers: qcolombet, dsanders, bogner, aemerson, javed.absar

Reviewed By: qcolombet

Subscribers: rovka, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D44700

llvm-svn: 333053