lib: Kconfig: fix PHANDLE_CHECK_SEQ position outside of menu

CONFIG_PHANDLE_CHECK_SEQ is outside of the menu 'Library routines'
thus it's invisible in menuconfig and cannot be selected.
Fix this by moving the 'endmenu' after the PHANDLE_CHECK_SEQ definition

Fixes: c589132a ("fdt: Use phandle to distinguish DT nodes with same name")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>