Add support for sm_90a in <nv/target> API

[ahendriksen]

The new API be used as follows:

__global__ void kernel(int *out) {
    NV_DISPATCH_TARGET(
        NV_HAS_FEATURE_SM_90a, (
        *out = 901;
    ), NV_PROVIDES_SM_90, (
        *out = 900;
    ), NV_IS_DEVICE, (
        *out = 0;
    ));
}

Description

closes #1270

Checklist

• New or existing tests cover these changes. How to test?? I made this godbolt example to see that it works correctly.
• The documentation is up to date with these changes. See [DOC]: nv/target #1306

[wmaxey]

The solution looks fine to me. As long as this is strictly an NVCC concern then I'm happy with this. Thanks for taking the initiative to plug support in.

[ahendriksen]

IIUC, nvc++ does not support emitting SM90a code (I think it doesn't have the command-line parameters to specify sm90a?). So this PR supports all compilers to the maximum extent possible.

[ahendriksen]

Can we merge this PR?