Convert CONFIG_TIMESTAMP to Kconfig

This converts the following to Kconfig:
   CONFIG_TIMESTAMP

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/armv8/fsl-layerscape/Kconfig b/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
index da53afc..9bb870d 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
+++ b/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
@@ -21,6 +21,7 @@
 	select SYS_I2C_MXC_I2C1 if !DM_I2C
 	select SYS_I2C_MXC_I2C2 if !DM_I2C
 	imply PANIC_HANG
+	imply TIMESTAMP
 
 config ARCH_LS1028A
 	bool