docs: move the Juno-specific build option to Arm build option file

Moved the Juno-specific build option from the common build option
file to the Arm build option file.

Change-Id: I0f53203f0cfca4a3baadab2cee4339c9694cfe8b
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
2 files changed