[ARM] Correct handling of LSL #0 in an IT block

The check for LSL #0 in an IT block was checking if operand 4 was zero, but
operand 4 is the condition code operand so it was actually checking for LSLEQ.
Fix this by checking operand 3, which really is the immediate operand, and add
some tests.

Differential Revision: https://reviews.llvm.org/D30692

llvm-svn: 297142