Convert the flag swiotlb_force from an int to an enum, to prepare for
the advent of more possible values.
Suggested-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>