feat(spm): use platform option for faster build

Where possible, add the `PLATFORM` build option for a faster
build of hafnium of for FVP and TC platforms.
This generates a single SPMC binary, rather than all
other test artefacts generated by Hafnium's buildsystem.

There were setups which required the binary of Hafnium as the
hypervisor. For those created a new configuration `fvp-spm-hyp`,
which builds all targets.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Ic1181f0d7e3adeaf5e53fb3a11e56de26c066f0e
diff --git a/spm_config/fvp-disable_assertions b/spm_config/fvp-disable_assertions
index 206df94..8934961 100644
--- a/spm_config/fvp-disable_assertions
+++ b/spm_config/fvp-disable_assertions
@@ -1,2 +1,3 @@
 PROJECT=reference
+PLATFORM=secure_aem_v8a_fvp_vhe
 ENABLE_ASSERTIONS=0