[PATCH] Implement mad_hi built-in

We already have a working mul_hi, and the spec gives us the implementation as:
Returns mul_hi(a,b)+c.

Signed-off-by: Aaron Watry <awatry@gmail.com>

We already have a working mul_hi, and the spec gives us the implementation as:
Returns mul_hi(a,b)+c.

Signed-off-by: Aaron Watry <awatry@gmail.com>

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>