sunxi: don't enable ARMTHUMB XZ BCJ filter in kernel

Having CONFIG_XZ_DEC_ARMTHUMB enabled breaks squashfs when ARM BCJ
filter was used to create the filesystem (and that's what we do on
all ARM targets). Thus unset CONFIG_XZ_DEC_ARMTHUMB to fix
squashfs on sunxi.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

SVN-Revision: 45347