genpd: Makefile: build imx

The imx genpd was missed to be built out, add it in Makefile

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/genpd/Makefile b/drivers/genpd/Makefile
index c429485..6667536 100644
--- a/drivers/genpd/Makefile
+++ b/drivers/genpd/Makefile
@@ -3,6 +3,7 @@
 obj-y					+= amlogic/
 obj-y					+= apple/
 obj-y					+= bcm/
+obj-y					+= imx/
 obj-y					+= mediatek/
 obj-y					+= qcom/
 obj-y					+= renesas/