fix(pie): do not skip __RW_END__ address during relocation

In fixup_gdt_reloc(), do not skip the last address (__RW_END__) for
dynamic relocations.
Else, the invalidation of the data done under _init_c_runtime in
el3_entrypoint_common macro will not be correct.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I1166a59ac964ec8ad4e099cb3600e843afc71d82
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/225705


Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@foss.st.com>
Reviewed-by: Sebastien PASDELOUP <sebastien.pasdeloup-ext@st.com>