linker_script: move more common code to bl_common.ld.h

These are mostly used to collect data from special structure,
and repeated in many linker scripts.

To differentiate the alignment size between aarch32/aarch64, I added
a new macro STRUCT_ALIGN.

While I moved the PMF_SVC_DESCS, I dropped #if ENABLE_PMF conditional.
As you can see in include/lib/pmf/pmf_helpers.h, PMF_REGISTER_SERVICE*
are no-op when ENABLE_PMF=0. So, pmf_svc_descs and pmf_timestamp_array
data are not populated.

Change-Id: I3f4ab7fa18f76339f1789103407ba76bda7e56d0
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>