imx: remove imx sip file

We have switch to use arm_smccc_smc, no need to keep i.MX specific
sip wrapper.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/Makefile b/arch/arm/mach-imx/Makefile
index a70d51b..1aa26a5 100644
--- a/arch/arm/mach-imx/Makefile
+++ b/arch/arm/mach-imx/Makefile
@@ -218,7 +218,7 @@
 
 targets += $(addprefix ../../../,SPL spl/u-boot-spl.cfgout u-boot-dtb.cfgout u-boot.cfgout u-boot.uim spl/u-boot-nand-spl.imx)
 
-obj-$(CONFIG_ARM64) += lowlevel.o sip.o
+obj-$(CONFIG_ARM64) += lowlevel.o
 
 obj-$(CONFIG_MX5) += mx5/
 obj-$(CONFIG_MX6) += mx6/