Fix mesa dependency on older SLE

[Mystro256]

We don't build mesa for older SLE, so we should allow it to fall back to the distro provided package if it's unavailable.

Some caveats/notes:

• Distro mesa is often older, which doesn't have newer HW support... this patch might have zypper consider the two dependencies as of equal value, rather than the mesa-amdgpu as better. I don't think there's a way to do this with the default configuration of zypper
• Mariner also has this issue, as the OS vendor prefers to build mesa, but I don't know the package name yet as they haven't enabled the va drivers in their mesa yet
• I don't know if this is a temporary workaround for SLE yet, but we need this cherry-picked into 6.2 if accepted at the very least

[Mystro256]

Sorry for the noise, looks like we don't even support 15sp4 in ROCm 6.2, so this patch is invalid. I will follow up with a patch on Mariner once I find out more information.