AsciiFromHex is a function converts a hex number to an ASCII character. This function is used across multiple generators, so add it to the TableHelperLib. Signed-off-by: Pierre Gondois <pierre.gondois@arm.com> Signed-off-by: Sami Mujawar <sami.mujawar@arm.com> Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>