Convert CONFIG_BOOTP_SERVERIP to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTP_SERVERIP

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-stm32mp/Kconfig b/arch/arm/mach-stm32mp/Kconfig
index a6c7fc5..06ac349 100644
--- a/arch/arm/mach-stm32mp/Kconfig
+++ b/arch/arm/mach-stm32mp/Kconfig
@@ -173,6 +173,7 @@
 	bool "STM32 Extended TrustZone Protection"
 	depends on STM32MP15x
 	default y
+	imply BOOTP_SERVERIP
 	help
 	  Say y to enable STM32 Extended TrustZone Protection