codecs: update for check ifeq ($(TARGET_ARCH),arm)

This condition check will only pass when compile for 32bit platform.
It will not pass when generate the 32bit binary or libarary for 64bit platform.
update it with variants like LOCAL_SRC_FILES_arm to make it used by
32bit binary or library on 64biy platform as well

Change-Id: Ia887610a97c68fa58925d2d86c5eb29cb397d6ef
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>