xen/arm: tee: place OP-TEE Kconfig option right after TEE

It is nicer, when options for particular TEE mediators (currently,
OP-TEE only) are following generic "Enable TEE mediators support"
option in the menuconfig:

 [*] Enable TEE mediators support
 [ ]   Enable OP-TEE mediator

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>

xen/arch/arm/Kconfig

@@ -113,6 +113,8 @@ config TEE
 	  This option enables generic TEE mediators support. It allows guests
 	  to access real TEE via one of TEE mediators implemented in XEN.
 
+source "arch/arm/tee/Kconfig"
+
 endmenu
 
 menu "ARM errata workaround via the alternative framework"
@@ -238,5 +240,3 @@ source "arch/arm/platforms/Kconfig"
 source "common/Kconfig"
 
 source "drivers/Kconfig"
-
-source "arch/arm/tee/Kconfig"