Revert "alpha-softmmu: Disable for the 0.15 release branch."

This reverts commit 46f08792.

This was not supposed to be applied to mainline.
Signed-off-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

configure

@@ -855,6 +855,7 @@ if [ "$softmmu" = "yes" ] ; then
     default_target_list="\
 i386-softmmu \
 x86_64-softmmu \
+alpha-softmmu \
 arm-softmmu \
 cris-softmmu \
 lm32-softmmu \