v3dv/device: clarify that we can't expose textureCompressionBC

From spec:

"textureCompressionBC specifies whether all of the BC compressed
 texture formats are supported. If this feature is enabled"

Note the *all*. v3d hw supports BC1, BC2, and BC3, but not BC4 through
BC7.

Let's clarify that we can't expose textureCompressionBC even if we
support some of them.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <!8929>

src/broadcom/vulkan/v3dv_device.c

@@ -857,6 +857,10 @@ v3dv_GetPhysicalDeviceFeatures(VkPhysicalDevice physicalDevice,
       .samplerAnisotropy = true,
       .textureCompressionETC2 = true,
       .textureCompressionASTC_LDR = false,
+      /* Note that textureCompressionBC requires that the driver support all
+       * the BC formats. V3D 4.2 only support the BC1-3, so we can't claim
+       * that we support it.
+       */
       .textureCompressionBC = false,
       .occlusionQueryPrecise = true,
       .pipelineStatisticsQuery = false,