arm64: perf: Rename Cortex A57 events

The implemented Cortex A57 events are strictly-speaking not
A57 specific. They are ARM recommended implementation defined events
and can be found on other ARMv8 SOCs like Cavium ThunderX too.

Therefore rename these events to allow using them in other
implementations too.

Signed-off-by: Jan Glauber <jglauber@cavium.com>
[will: capitalisation and ordering]
Signed-off-by: Will Deacon <will.deacon@arm.com>