graphics/mesa-dri: don't forbid WAYLAND on non-x86

At least aarch64, armv6, armv7 couldn't set OPTIONS_SET+=WAYLAND via make.conf
(see also bug 227509) despite Wayland itself not having such a limitation.

>> Ignoring graphics/mesa-dri: option WAYLAND is only valid on platforms with Vulkan

PR: 221540
Pointy hat to: jbeich (regressed by r482192)