juno: Remove -Os/-flto for debug mode

New adjustments to the maximum size of the SCP_BL2 image in Trusted
Firmware-A means we now have far greater room for expansion.

Change-Id: I9bc4791e5a2347f2d30bdcb3a482b5a3e6801e0a
Signed-off-by: Chris Kay <chris.kay@arm.com>