build_helpers: Change Reg test for TC3 to Release mode

The current regression tests for TC3 cover the debug builds,
but it's too verbose, so replace it with a Release build.

Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Change-Id: I2cb2ff1c312f3a5590b8fac589f51e3d5778eb11
1 file changed