In LCD Display,scrolling only one line
The HD44780 LCD driver considers the display as 80 contiguous characters; it's not aware of the concept "character lines". A 16x2 display is for the HD44780 the same as a 32x1 display.  

So no, you can't scroll one line and leave the other one static. You'll have to rewrite the whole display contents.

edit
Good point by Myforwik: in that 80 character string the characters shown in line 1 and 2 may not be contiguous. The first line will often be 40 characters, with for instance 16 visible, and then the second line will start at the 41st character.