refactor(sptool): use SpSetupActions in sp_mk_generator.py

refactor(sptool): use SpSetupActions in sp_mk_generator.py

The "sp_mk_generator.py" is responsible for processing the SP layout
file, which contains information about the SPs to be deployed on top of
the SPM, to generate the "sp_gen.mk" file which appends information
specific to each SP that shall help with packing all SPs into a fip
binary.
Before this patch the "sp_mk_generator.py" was a monolithic script,
which has now been broken down into functions for each identified
configuration action.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I8ee7487f2e07d53e508d17d0fe4510e22957f5ca