perf_events, x86: Fixup fixed counter constraints

Patch 1da53e02 ("perf_events, x86: Improve x86 event scheduling")
lost us one of the fixed purpose counters and then ed8777fc
("perf_events, x86: Fix event constraint masks") broke it even
further.

Widen the fixed event mask to event+umask and specify the full config
for each of the 3 fixed purpose counters. Then let the init code fill
out the placement for the GP regs based on the cpuid info.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>