perf: Add ability to attach user level registers dump to sample

Introducing PERF_SAMPLE_REGS_USER sample type bit to trigger the dump of
user level registers on sample. Registers we want to dump are specified
by sample_regs_user bitmask.

Only user level registers are dumped at the moment. Meaning the register
values of the user space context as it was before the user entered the
kernel for whatever reason (syscall, irq, exception, or a PMI happening
in userspace).

The layout of the sample_regs_user bitmap is described in
asm/perf_regs.h for archs that support register dump.

This is going to be useful to bring Dwarf CFI based stack unwinding on
top of samples.

Original-patch-by: Frederic Weisbecker <[email protected]>
[ Dump registers ABI specification. ]
Signed-off-by: Jiri Olsa <[email protected]>
Suggested-by: Stephane Eranian <[email protected]>
Cc: "Frank Ch. Eigler" <[email protected]>
Cc: Arun Sharma <[email protected]>
Cc: Benjamin Redelings <[email protected]>
Cc: Corey Ashford <[email protected]>
Cc: Cyrill Gorcunov <[email protected]>
Cc: Frank Ch. Eigler <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Tom Zanussi <[email protected]>
Cc: Ulrich Drepper <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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