perf/x86/amd/ibs: Add bitfield definitions in new <asm/amd-ibs.h> header

Add <asm/amd-ibs.h> with bitfield definitions for IBS MSRs,
and demonstrate usage within the driver.

Also move 'struct perf_ibs_data' where it can be shared with
the perf tool that will soon be using it.

No functional changes.

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210817221048.88063-9-kim.phillips@amd.com