Add Hexagon packet support to ThreadPlanStepRange

Summary:
Hexagon is a VLIW processor. It can execute multiple instructions at once, called a packet. Breakpoints need to be alone in a packet. This patch will make sure that temporary breakpoints used for stepping are set at the start of a packet, which will put the breakpoint in a packet by itself.

Patch by Deepak Panickal of CodePlay and Ted Woodward of Qualcomm.

Reviewers: deepak2427, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9437

llvm-svn: 237047