aemfvp-a-rme: adding realm distro usecase for 2024.04.15 release

For a distro to boot in realm security state the stock kernel in
distro image has to be updated with a cca aware kernel that we
are building as part of building this stack.
Updates include
- adding update_debs flag in distro.sh to update the cca aware kernel
  in distro image with sudo dpkg -i.
- automate_distro_realm_boot.sh script aims to automate distro realm
  boot preperation steps.
  1. Building the stack with LINUX_BUILD_DEB_PKG=1 to create debs
  2. Copying the linux debs over to distro image's Linux filesystem
    section with utils/distro_kernel_debs_copy.sh
  3. Booting distro fvp and updating the default kernel with sudo
    dkpg using utils/distro_dpkg_update.sh
  4. Rebuilding the buildroot section of stack to pack the cca kernel
    distro image in host's filesystem using rebuild_buildroot.sh
  5. Checking distro image can be booted in realm security state
     with realm_distro_boot.sh
- adding 30 sec delay to ensure network stack is initialised before ping.

Signed-off-by: nitin sharma <nitin.sharma3@arm.com>
Change-Id: I5e9e217b9d50b7aa889e6262d01a2b16e067c3a6