fix(smc): correctly find pmf version

Commit@f7679d437d5f27a3168f017db8d42bc561ac0c59
PMF is moved under vendor specific EL3 range, part of this
we have introduced each sub-service have an version scheme[1].

- Current PMF is not handling correctly identifying all FID's
  under it so handle this correctly.
- Minor refactor to use existing macro GET_SMC_NUM rather than manual
  parsing to find the SMC number.

[1]:
https://trustedfirmware-a.readthedocs.io/en/latest/components/ven-el3-service.html



Change-Id: I7a4c8936e42d4a579f0243fa3d06015540caca37
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>