arm64: efi: Export screen_info

The Hyper-V frame buffer driver may be built as a module, and
it needs access to screen_info. So export screen_info.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1628092359-61351-5-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>