chore(docs): remove hafnium specific documentation

All the relevant documentation for Hafnium as the chosen Secure
Partition Manager has been moved to hafnium project[1].

This patch removes the redundant sections without any loss of
information.

This patch adds links to documentation of each of the SPM projects.

[1] https://hafnium.readthedocs.io/en/latest/secure-partition-manager/index.html

Change-Id: I52caf7dc50f4aa253c68309cac0915b7d368939d
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
1 file changed