Do not store fp and sp values in TickSample

Do not store fp and sp values in TickSample

Their values are not used neither by the tick processor nor by CpuProfiler so it is just a waste of space.

TickSample used to be a transport for grabbed register values to TickSample::Trace, now they are passed in a special structure RegisterState which is allocated on the stack for the sampling period.

Some common pieces were moved from platform-dependent code into Sampler::SampleStack and TickSample::Init.

BUG=None
R=jkummerow@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/18620002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15484 ce2b1a6d-e550-0410-aec6-3dcde31c8c00