Add padding for the interpreter registers when needed, to make the
interpreter frame a multiple of 16 bytes. The padding needs to be added
in the InterpreterEntryTrampoline and when generating an interpreter
frame in the deoptimizer. It also needs to be considered when
calculating the size of the interpreter frame during OSR and stack
unwinding.

Bug: v8:6644
Change-Id: Icfec94079cf0785fc8a2506ff555b5f9e89e3d13
Reviewed-on: https://chromium-review.googlesource.com/664563
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48121}