support/config-fragments/autobuild: fix riscv toolchains

support/config-fragments/autobuild: fix riscv toolchains

In commit aee39cbf27e (arch/riscv: set the default float ABI based on
ISA extensions), the default ABI changed, so the config fragments used
by the autobuilders were adapated accordingly, in commit f89871e81085
(support/config-fragments: fix br-riscv{32,64} toolchain fragments).

But now, we need to revert again, because the newer toolchains are now
using the default ABI again.

We do not really do a revert, though, because the original change was
right, and a revert would mean it was not.

Fixes:
    http://autobuild.buildroot.org/results/b59/b593267fb9fc9a002b977e049b2a5389dbaded30/ (riscv32)
    http://autobuild.buildroot.org/results/b42/b42a4b22b29f47d5c85be119b310f1dfb61112a1/ (riscv64)
    ... and so many others on various packages...

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Mark Corbin <mark.corbin@embecosm.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>