30/08/2021:dotprod.f90, optimisation for GPU , add kernels + loop independent

src/ZSOLVER/dotprod.f90

@@ -168,14 +168,18 @@ ENDIF
 !
 !JUAN16
 ALLOCATE(ZDOTPROD(ILBXB:ILBXE,ILBYB:ILBYE))
+!$acc kernels
 ZDOTPROD    = 0.
+!$acc loop seq
 DO JK = IKB-1,IKE+1
+   !$acc loop independent collapse(2) 
    DO JJ = ILBYB,ILBYE
       DO JI = ILBXB,ILBXE
          ZDOTPROD(JI,JJ) = ZDOTPROD(JI,JJ) + PA(JI,JJ,JK) * PB(JI,JJ,JK)
       END DO
    END DO
 END DO
+!$acc end kernels
 PDOTPROD = SUM_DD_R2_ll(ZDOTPROD)
 !JUAN16
 !