modinv AVX2: do quick norm on result twice and convert 32-bit signed to 64-bit signed before adding P-256 mont_add, mont_dbl, mont_tpl, mont_sub x64: handle mul/sqr result being greater than modulus but not greater than 1<<256.
modinv AVX2: do quick norm on result twice and convert 32-bit signed to 64-bit signed before adding P-256 mont_add, mont_dbl, mont_tpl, mont_sub x64: handle mul/sqr result being greater than modulus but not greater than 1<<256.