gstreamer1: fix xtensa configure

Disable unaligned access to avoid configure run test.

Fixes
http://autobuild.buildroot.net/results/1fb/1fb5bde77ea84f13fe8db7dedda5b8a29671b939/

.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>