imx8m: rename clock to clock_imx8mq

i.MX8MQ and i.MX8MM has totally different pll design, so
rename clock to clock_imx8mq.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/Makefile b/arch/arm/mach-imx/imx8m/Makefile
index feff494..42a1544 100644
--- a/arch/arm/mach-imx/imx8m/Makefile
+++ b/arch/arm/mach-imx/imx8m/Makefile
@@ -3,4 +3,5 @@
 # Copyright 2017 NXP
 
 obj-y += lowlevel_init.o
-obj-y += clock.o clock_slice.o soc.o
+obj-y += clock_slice.o soc.o
+obj-$(CONFIG_IMX8MQ) += clock_imx8mq.o