x86: make vmmouse optional

Compile vmmouse in hwlib. Ignore failure if vmmouse device can't be
created.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/default-configs/x86_64-softmmu.mak b/default-configs/x86_64-softmmu.mak
index eff26d2..daf8c48 100644
--- a/default-configs/x86_64-softmmu.mak
+++ b/default-configs/x86_64-softmmu.mak
@@ -4,6 +4,7 @@
 CONFIG_VGA_PCI=y
 CONFIG_VGA_ISA=y
 CONFIG_VMWARE_VGA=y
+CONFIG_VMMMOUSE=y
 CONFIG_SERIAL=y
 CONFIG_PARALLEL=y
 CONFIG_I8254=y