MIPS: ath79: don't hardcode the unavailability of the DSP ASE

The ath79 platform code allows to run a single kernel image on various
SoCs which are based on the 24Kc and 74Kc cores.  The current code
explicitely disables the DSP ASE, but that is available in the 74Kc core.

Remove the override in order to let the kernel to detect the availability
of the DSP ASE at runtime.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/4222/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>