arm64: Fix finding the pmc event ID

The lower pmc event bits were masked off to find the PMC event ID.
The doesn't work when there are more events. Switch it to use the
offser relative to the first event while also checking the ID is
in the expected range.

Reviewed by:	gnn, ray
Sponsored by:	Innovate UK
Differential Revision:	https://reviews.freebsd.org/D29600

sys/dev/hwpmc/hwpmc_arm64.c

@@ -181,7 +181,9 @@ arm64_allocate_pmc(int cpu, int ri, struct pmc *pm,
 	}
 	pe = a->pm_ev;
 
-	config = (pe & EVENT_ID_MASK);
+	config = (uint32_t)pe - PMC_EV_ARMV8_FIRST;
+	if (config > (PMC_EV_ARMV8_LAST - PMC_EV_ARMV8_FIRST))
+		return (EINVAL);
 	pm->pm_md.pm_arm64.pm_arm64_evsel = config;
 
 	PMCDBG2(MDP, ALL, 2, "arm64-allocate ri=%d -> config=0x%x", ri, config);

sys/dev/hwpmc/hwpmc_arm64.h

@@ -40,7 +40,6 @@
 
 #define	ARMV8_RELOAD_COUNT_TO_PERFCTR_VALUE(R)	(-(R))
 #define	ARMV8_PERFCTR_VALUE_TO_RELOAD_COUNT(P)	(-(P))
-#define	EVENT_ID_MASK	0xFF
 
 #ifdef _KERNEL
 /* MD extension for 'struct pmc' */