Kconfig: move NXP specific stuff into a sub-menu

Having NXP specific items in the main menu is confusing. Especially
the comment line

   *** Other functionality shared between NXP SoCs ***

is simply misleading.

Move all NXP stuff into a separate sub-menu.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/arch/Kconfig.nxp b/arch/Kconfig.nxp
index ad61dab..f492b04 100644
--- a/arch/Kconfig.nxp
+++ b/arch/Kconfig.nxp
@@ -1,3 +1,5 @@
+menu "Functionality shared between NXP SoCs"
+
 config FSL_TRUST_ARCH_v1
 	bool
 
@@ -142,8 +144,6 @@
 
 endmenu
 
-comment "Other functionality shared between NXP SoCs"
-
 config DEEP_SLEEP
 	bool "Enable SoC deep sleep feature"
 	depends on ARCH_T1024 || ARCH_T1040 || ARCH_T1042 || ARCH_LS1021A
@@ -271,3 +271,5 @@
 
 config SYS_DPAA_FMAN
 	bool
+
+endmenu