Compile i8254 only once

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/default-configs/mips64el-softmmu.mak b/default-configs/mips64el-softmmu.mak
index 4e6830c..641db27 100644
--- a/default-configs/mips64el-softmmu.mak
+++ b/default-configs/mips64el-softmmu.mak
@@ -4,3 +4,4 @@
 CONFIG_ESP=y
 CONFIG_VGA_PCI=y
 CONFIG_PARALLEL=y
+CONFIG_I8254=y