arm64: perf: Treat EXCLUDE_EL* bit definitions as unsigned

Although the upper 32 bits of the PMEVTYPER<n>_EL0 registers are RES0,
we should treat the EXCLUDE_EL* bit definitions as unsigned so that we
avoid accidentally sign-extending the privilege filtering bit (bit 31)
into the upper half of the register.

Signed-off-by: Will Deacon <will.deacon@arm.com>