Add PIE support for AARCH32

Only BL32 (SP_min) is supported at the moment, BL1 and BL2_AT_EL3 are just
stubbed with _pie_fixup_size=0.
The changes are an adaptation for AARCH32 on what has been done for
AARCH64.
The RELA_SECTION is redefined for AARCH32, as the created section is
.rel.dyn and the symbols are .rel*.
In BL32 linker script, .dynsym .dynstr .hash .gnu.hash are discarded.
And no more used __BSS_SIZE__  and __COHERENT_RAM_UNALIGNED_SIZE__
symbols are removed.

Change-Id: I92bafe70e6b77735f6f890f32f2b637b98cf01b9
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/175515


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@st.com>