R600: Add udivrem test

v2: move < %s to the end of the line
    space after ;
    add v4i32 test

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
R600: Implement custom SDIVREM.

Instead of separate SDIV/SREM. SDIV used UDIV which in turn used UDIVREM anyway.
SREM used SDIV(UDIV->UDIVREM)+MUL+SUB, using UDIVREM directly is more efficient.

v2: Don't use all caps names

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
R600: Use LowerSDIVREM for i64 node replace

v2: move div/rem node replacement to R600ISelLowering
    make lowerSDIVREM protected

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>