refactor(smccc): move debugfs to vendor el3 calls

Move debugfs to Vendor-Specific EL3 Monitor Service Calls.
Function Identifier for Vendor-Specific EL3 Monitor Service is '7' and
allocated subranges of Function identifiers to different services are:

0x87000000-0x8700FFFF-SMC32: Vendor-Specific EL3 Monitor Service Calls
0xC7000000-0xC700FFFF-SMC64: Vendor-Specific EL3 Monitor Service Calls

Amend Debugfs FID's to use this range and id.

Add a deprecation notice to inform debugfs moved from arm-sip range to
Vendor-Specific EL3 range. Debugfs support from arm-sip range will be
removed and will not be available after TF-A 2.12 release.

Reference to debugfs component level documentation:
https://trustedfirmware-a.readthedocs.io/en/latest/components/debugfs-design.html#overview

Change-Id: I97a50170178f361f70c95ed0049bc4e278de59d7
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/docs/components/index.rst b/docs/components/index.rst
index 36ab6fa..18522f8 100644
--- a/docs/components/index.rst
+++ b/docs/components/index.rst
@@ -27,3 +27,4 @@
    rmm-el3-comms-spec
    granule-protection-tables-design
    ven-el3-service
+   ven-el3-debugfs