[build] Include Hyper-V driver in the all-drivers build

Signed-off-by: Michael Brown <mcb30@ipxe.org>
diff --git a/src/arch/x86/Makefile b/src/arch/x86/Makefile
index a0fee39..1751c0c 100644
--- a/src/arch/x86/Makefile
+++ b/src/arch/x86/Makefile
@@ -16,3 +16,7 @@
 
 # disable valgrind
 CFLAGS		+= -DNVALGRIND
+
+# Include Hyper-V driver in the all-drivers build
+#
+DRIVERS += hyperv