Use #ifdef for AARCH32 instead of #if

Use #ifdef for AARCH32 instead of #if

One nasty part of ATF is some of boolean macros are always defined
as 1 or 0, and the rest of them are only defined under certain
conditions.

For the former group, "#if FOO" or "#if !FOO" must be used because
"#ifdef FOO" is always true.  (Options passed by $(call add_define,)
are the cases.)

For the latter, "#ifdef FOO" or "#ifndef FOO" should be used because
checking the value of an undefined macro is strange.

For AARCH32/AARCH64, these macros are defined in the top-level
Makefile as follows:

ifeq (${ARCH},aarch32)
        $(eval $(call add_define,AARCH32))
else
        $(eval $(call add_define,AARCH64))
endif

This means only one of the two is defined.  So, AARCH32/AARCH64
belongs to the latter group where we should use #ifdef or #ifndef.
The conditionals are mostly coded correctly, but I see some mistakes.

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