Switch zero point of negate to input variable type

This commit changes the zero point attribute to an input to align
with the 1.0 spec.
Also marks both as CTC (Compile Time Constants) and enables
EXT-DYNAMIC tests.

Change-Id: I175c45a0f25470fbef5d2c2087bf882fb7fcf46d
Signed-off-by: Luke Hutton <luke.hutton@arm.com>
Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Co-authored-by: Jeremy Johnson <jeremy.johnson@arm.com>