Fround fixes

Created by: jordancarlin

• Add tests for fround.d and froundnx
• Update control bits to correctly assert ZfaFRoundNXD
• Update floating-point fmt detection to work for fround class of instructions
• Modify TMask to give correct sticky bit when X == 1 by swapping the order of the inversion and right shift

With the inclusion of tests for fround.d and froundnx, fround coverage is up to 94.44% with 17/18 expressions covered.