(Vulkan) Can't take screenshots when HDR is enabled

[LibretroAdmin]

hi @MajorPainTheCactus ,

We noticed that taking screenshots with the vulkan driver with HDR enabled currently doesn't work. Tracked it down to line 3397
of vulkan.c -

'Unexpected swapchain format'

The swapchain format that it uses for HDR10 needs an implementation. Could you look into this? This format is among the ones not catered to right now -

VK_FORMAT_A2B10G10R10_UNORM_PACK32