configs: migrate from 8.3 to 10.2 GNU Toolchain

GNU v8.3 compiler has been used to compile the platform software. As
there is an oppurtunity to migrate to the latest toolchain version,
switch to using GNU v10.2 toolchain. There are changes in the toolchain
naming format as well and so accomodate those changes as well.

Signed-off-by: Zakaria Zahi <zakaria.zahi@arm.com>
Change-Id: Ie8f0a75e879392d9f3f2e966d268db9b9b2bf63e