[mlir] Fix nvvm integration tests build error (#70113)

#69934 broke integration tests that rely on the
kernel-bare-ptr-calling-convention and host-bare-ptr-calling-convention
flags. This PR brings these flags.

Also the kernel-index-bitwidth flag is removed, as kernel pointer size
depends on the host. Separating host (64-bit) and kernel (32-bit) is not
viable.