arm64/perf: Changed events naming as per the ARM ARM

changed all the common events name definition as per the document
ARM DDI 0487A.g

SoC specific event names follow the general naming style in
the file and doesn't reflect any document.
changed ARMV8_A53_PERFCTR_PREFETCH_LINEFILL to
ARMV8_A53_PERFCTR_PREF_LINEFILL to match with other SoC specific
event names which use _PREF_ style.

corrected typo l21 to l2i.

Signed-off-by: Ashok Kumar <ashoks@broadcom.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>