Compile vga-isa only once

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/default-configs/mips64-softmmu.mak b/default-configs/mips64-softmmu.mak
index 8dffae9..4e204a4 100644
--- a/default-configs/mips64-softmmu.mak
+++ b/default-configs/mips64-softmmu.mak
@@ -3,6 +3,7 @@
 CONFIG_ISA_MMIO=y
 CONFIG_ESP=y
 CONFIG_VGA_PCI=y
+CONFIG_VGA_ISA=y
 CONFIG_PARALLEL=y
 CONFIG_I8254=y
 CONFIG_PCSPK=y