bl32: sp_min: reduce the alignment for fconf_populator

sp_min.ld.S is used for aarch32.

ALIGN(4) is used for alignment of the other structures. I do not think
struct fconf_populator is a special case. Let's use ALIGN(4) here too.

Perhaps, this is just a copy-paste mistake of commit 26d1e0c3
("fconf: necessary modifications to support fconf in BL31 & SP_MIN").

Change-Id: I29f4c68680842c1b5ef913934b4ccf378e9bfcfb
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>