VSETC defines from xs1.h should be used where possible

[xross]

VSETC defines from xs1.h should be used where possible to configure the vector unit instead of magic numbers in the asm i.e : https://github.com/xmos/ai_tools/blob/21c73b9edee1fce8216adeac82cb0c5a3a4a0052/lib_nn/lib_nn/src/asm/bsign_8.S#L46-L47

The following commits should mean these are available in a subsequent tools release:

• https://github0.xmos.com/xmos-int/tools_xmosutils/commit/e843239f9e0fbb55ec2014fb57a87a4ec430fa8b
• https://github0.xmos.com/xmos-int/tools_xmosutils/commit/e4e76b94fd30e05b80854f46648a71909bcd5721