lv_sqrt() function

integer which square root should be calculated

store the result here. q->i: integer part, q->f: fractional part in 1/256 unit

optional to skip some iterations if the magnitude of the root is known. Set to 0x8000 by default. If root < 16: mask = 0x80 If root < 256: mask = 0x800 Else: mask = 0x8000