This fixes an issue originally introduced with the BGEMM kernel.
I've updated the tests to run with `beta=1.0` so as to test loading and
updating from C.
Alongside this, the tests now return sensible return values to reduce
the risk of them being ignored.
Also fixed a bug in `generic/gemv_t.c` resulting in weird outputs for
`bgemv`.
This adds an SVE implementation to sdot/ddot when available, falling back to the previous Advanced SIMD kernel where there's no SVE implementation for the kernel.
All the targets were essentially treating `dot_thunderx2t99.c` as the Advanced SIMD implementation so I've renamed it to better fit with the feature detection.