anv: Advertise two more formats
These both require swizzling so border colors won't work. However, they're conveniently in the list of formats for which custom border colors require you to specify a format in the sampler. That list constists of:
- VK_FORMAT_B4G4R4A4_UNORM_PACK16
- VK_FORMAT_B5G6R5_UNORM_PACK16
- VK_FORMAT_B5G5R5A1_UNORM_PACK16
Closes: #6226 (closed)