[BSP][UBOOT][FIX] add build-time dependency gnutls-native

U-boot build fails with the following error:

  /home/yoctouser/workdir/build-imx8mpevk/tmp/work/nxp_imx8mpevk-poky-linux/u-boot-seco/2024.04/git/tools/mkeficapsule.c:20:10: fatal error: gnutls/gnutls.h: No such file or directory
     20 | #include <gnutls/gnutls.h>
        |          ^~~~~~~~~~~~~~~~~
  compilation terminated.

Add dependency gnutls-native to fix that.

CLEAOS-532

Signed-off-by: Alessandro Pecugi <alessandro.pecugi@seco.com>

recipes-bsp/u-boot-seco/u-boot-seco-imx.inc

 
 # DEPENDS += "rk-binary-native coreutils-native flex-native bison-native dtc-native"
-DEPENDS += "coreutils-native flex-native bison-native dtc-native"
+DEPENDS += "coreutils-native flex-native bison-native dtc-native gnutls-native"
 require recipes-bsp/u-boot/u-boot-seco.inc
 
 LICENSE = "GPLv2+"