[ARM][Driver] Fix i8mm feature string (#137771)
#137595 changed the behaviour for SIMD on ARM to ensure it is enabled
and disabled correctly depending on the options used by the user. In
this, the functionality to disable all features that depend on SIMD was
added. However, there was a spelling error for the i8mm feature, which
caused the `+nosimd` command to fail.
This fixes the error, and allows the command to work again.
