sgi/install_prerequisites.sh: add srecord to list of apt tools

srecord is required for using the `srec_cat` command while running
the upcoming build-tf-m.sh script to pack TF-M binaries. Add it to the
list of apt packages to install.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I6a7b561a8ba2b3bcab4ebd021372376ed00c7827