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/Kconfig b/arch/Kconfig
index ee32e83..f2deec1 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -256,6 +256,7 @@
 	imply ACPIGEN if !QEMU
 	imply SYSINFO if GENERATE_SMBIOS_TABLE
 	imply SYSINFO_SMBIOS if GENERATE_SMBIOS_TABLE
+	imply TIMESTAMP
 
 	# Thing to enable for when SPL/TPL are enabled: SPL
 	imply SPL_DM
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8fc1897..6b11c3a 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1869,6 +1869,7 @@
 	imply OF_LIBFDT_OVERLAY
 	imply ENV_VARS_UBOOT_RUNTIME_CONFIG
 	imply USE_PREBOOT
+	imply TIMESTAMP
 	help
 	  Support for STM32MP SoC family developed by STMicroelectronics,
 	  MPUs based on ARM cortex A core
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
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 4471754..c308447 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -381,6 +381,7 @@
 	imply CMD_PCI
 	imply CMD_REGINFO
 	imply FSL_SATA
+	imply TIMESTAMP
 
 config ARCH_P1011
 	bool
@@ -512,6 +513,7 @@
 	imply CMD_EEPROM
 	imply CMD_NAND
 	imply CMD_REGINFO
+	imply TIMESTAMP
 
 config ARCH_P2041
 	bool