mediatek: activate fpu feature flag

mediatek: activate fpu feature flag

The arm CPUs uses in the supported Mediatket SoCs have a FPU accordingly
to the datasheet, activate it also. The CPU subtype "neon-vfpv4" is
selected, but the toolcahin generated for this SoC will still be
compiled with soft float and not with the hard float ABI as we haven't
the fpu feature flag set. If this toolchain is reused by other targets
this will even affect other targets.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>