refactor(build): renaming BL2_AT_EL3 to RESET_TO_BL2

Along with e09da7be3fe5f7a59f16abc6008a8a97c3e1c247 that introduces a
breaking refactoring change we have to rename the build option in the CI
scripts.
Renaming BL2_AT_EL3 to RESET_TO_BL2.

Signed-off-by: Maksims Svecovs <maksims.svecovs@arm.com>
Change-Id: I57fe6c8e289a71d8d3cea3a6d71760d7df43112e
9 files changed