stm32mp: update dependency for STM32_ETZPC

Correct the dependency for STM32 ETZPC protection, linked to SOC
STM32MP identified by CONFIG_STM32MP15x and not linked to
CONFIG_TARGET_STM32MP1 (no more existing).

This patch fix an issue introduced by commit 846254888e2e ("stm32mp1:
split board and SOC support for STM32MP15x family").

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/mach-stm32mp/Kconfig b/arch/arm/mach-stm32mp/Kconfig
index e4d621d..9615369 100644
--- a/arch/arm/mach-stm32mp/Kconfig
+++ b/arch/arm/mach-stm32mp/Kconfig
@@ -119,7 +119,7 @@
 
 config STM32_ETZPC
 	bool "STM32 Extended TrustZone Protection"
-	depends on TARGET_STM32MP1
+	depends on STM32MP15x
 	default y
 	help
 	  Say y to enable STM32 Extended TrustZone Protection