R600: Implement 64bit SHL

v2: Use c++ style comment

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
R600: Implement 64bit SRL

v2: use C++ style comment

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
R600: Implement 64bit SRA

v2: Use capitalized variable name

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