spm: Remove SPM Alpha 1 prototype and support files

The Secure Partition Manager (SPM) prototype implementation is
being removed. This is preparatory work for putting in place a
dispatcher component that, in turn, enables partition managers
at S-EL2 / S-EL1.

This patch removes:

- The core service files (std_svc/spm)
- The Resource Descriptor headers (include/services)
- SPRT protocol support and service definitions
- SPCI protocol support and service definitions

Change-Id: Iaade6f6422eaf9a71187b1e2a4dffd7fb8766426
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
Signed-off-by: Artsem Artsemenka <artsem.artsemenka@arm.com>