automation: re-enable building SeaBIOS in Alpine container

It seems to build just fine with Alpine 3.12, and SeaBIOS is necessary
for a HVM test (that use the Alpine build).

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

automation/scripts/build

@@ -77,8 +77,6 @@ else
     if ldd /bin/ls | grep -q musl; then
         # disable --disable-werror for QEMUU when building with MUSL
         cfgargs+=("--with-extra-qemuu-configure-args=\"--disable-werror\"")
-        # SeaBIOS doesn't build on MUSL systems
-        cfgargs+=("--with-system-seabios=/bin/false")
     fi
 
     # Qemu requires Python 3.5 or later, and ninja