toolchain/toolchain-external/toolchain-external-bootlin: update PowerPC 440 FP toolchain

The Bootlin PowerPC 440 FP toolchain was rebuilt in version 2020.08-2,
which is rebased on Buildroot 2020.08.3 as that includes a fix for
SecurePLT support.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>