feat(rmm): report PMU not supported

This patch reports for PMU not being supported by RMM
and adds relevant definitions for Feature Register 0
in accordance with Beta 0 RMM Specification.
It also masks PMUVer field when ID_AA64DFR0_EL1
register is read by Realm.
ID_AA64DFR0_EL1 register mask and set values are
modified to report minimum Debug features supported
by ARM architecture.

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: I9974dac476df270f309f6bb30d3485ba0af5986e