mkimage: fix segfault on MacOS arm64

mkimage segfaults due to the ASLR mechanism on MacOS arm64

It is required to use _dyld_get_image_vmaddr_slide()
to prevent segfault on MacOS arm64

This patch is based on the discussion
https://github.com/u-boot/u-boot/commit/3b142045e8a7f0ab17b6099e9226296af45967d0



Thanks to Jessica Clarke, Ronny Kotzschmar and ptpt52 github user

Reviewed-by: Jessica Clarke <jrtc27@jrtc27.com>
Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>