Transceiver52M: Fix SSE convolution shuffle register

An errant shuffle register value used in complex-complex convolution
causes distorted correlation peak-to-average values for certain TSC
values. The error effect varies for different TSC sequences with the
most noticeable effect of degraded detection on TSC 1 and no effect on
TSC 7.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
Transceiver52M: Re-enable autoconf x86 arch detection

commit c13f8bde8f1d00f44cc854fa77b4196a733d7808 "merged in commercial
openbts" removed AC_CONFIG_MACRO_DIR in configure.ac, which in effect
disabled SSE support on environments where the detection macro, AX_EXT,
was not already present.

Rather than rely on AX_EXT be present in the distribution, use the
version that is already included with OpenBTS by re-enabling the config
m4 directory.

Signed-off-by: Thomas Tsou <tom@tsou.cc>