gst-fsl-plugin: Fix checking for include headers in multiple paths

gst-fsl-plugin: Fix checking for include headers in multiple paths

This fixes the support for proper detecting Freescale specific headers
in include/linux and include/uapi.

Without this patch I have the configure log with the same feature in
'enabled' and 'disabled' state and it was impossible to proper
override CPPFLAGS.

After this patch, building it against MX53 I get:

Configure result:
        Enabled features:
                plugin: aac_dec
                plugin: mp3_dec
                plugin: vorbis_dec
                plugin: amr_dec
                plugin: mp3_enc
                plugin: h264_dec
                plugin: mpeg4_dec
                plugin: mpeg2_dec
                plugin: aiur
                plugin: beep
                plugin: v4lsink
                plugin: isink
                plugin: ipucsc
                library: libipu
                library: libX11
        Disabled features:
                plugin: aacp_dec
                plugin: wma10_dec
                plugin: ac3_dec
                plugin: wma8_enc
                plugin: downmix
                plugin: wmv9mp_dec
                plugin: wmv78_dec
                plugin: vpu_wrap

and building it against MX6Q I get:

Configure result:
        Enabled features:
                plugin: aac_dec
                plugin: mp3_dec
                plugin: vorbis_dec
                plugin: amr_dec
                plugin: mp3_enc
                plugin: h264_dec
                plugin: mpeg4_dec
                plugin: mpeg2_dec
                plugin: vpu_wrap
                plugin: aiur
                plugin: beep
                plugin: v4lsink
                plugin: isink
                plugin: ipucsc
                library: libipu
                library: libX11
        Disabled features:
                plugin: aacp_dec
                plugin: wma10_dec
                plugin: ac3_dec
                plugin: wma8_enc
                plugin: downmix
                plugin: wmv9mp_dec
                plugin: wmv78_dec

Change-Id: Icdd40a1686212275b67baede34bb45eb41be3cf1
Reported-by: Jānis Čoders <janis.coders@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>