bl32: use SORT_BY_ALIGNMENT macro in sp_min.ld.S

The macro SORT_BY_ALIGNMENT is used for .text* and .rodata*. This allows
reducing the space lost to object alignment. This is an alignment with
the following patch:
ebd6efae

Some comments are also aligned with other linker scripts.

Change-Id: I2ea59edb445af0ed8c08fd883ffbf56852570d0c
Signed-off-by: Yann Gautier <yann.gautier@st.com>