imx8ulp: add upower api support

Add upower api support, this is modified from upower firmware exported
package.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8ulp/Makefile b/arch/arm/mach-imx/imx8ulp/Makefile
index 1ef6cd5..2c9938f 100644
--- a/arch/arm/mach-imx/imx8ulp/Makefile
+++ b/arch/arm/mach-imx/imx8ulp/Makefile
@@ -5,3 +5,7 @@
 
 obj-y += lowlevel_init.o
 obj-y += soc.o clock.o iomux.o pcc.o cgc.o rdc.o
+
+ifeq ($(CONFIG_SPL_BUILD),y)
+obj-y += upower/
+endif