arm64: sysreg: add debug system registers

This patch adds sysreg definitions for system registers in the debug and
trace system register encoding space. Subsequent patches will make use
of these definitions.

The encodings were taken from ARM DDI 0487A.k_iss10775, Table C5-5.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>