{Assembler::Nop} currently fails if {n} is bigger than {kGap} (the
destructor of {EnsureSpace} checks that not more than {kGap} bytes have
been emitted).
This CL fixes this by repeatedly using {EnsureSpace}, and also
optimizes the implementation of {Assembler::Nop} a bit.
It also removes stray cases for 10 and 11 nop bytes which have been
added in https://crrev.com/8773039 without further comment, and are not
documented in the Intel manual.

R=mstarzinger@chromium.org

Bug: v8:9477
Change-Id: I07bbe311d2daa75dc27b91a0ccb503427c52841f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1708476
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62808}