ArmPlatformPkg/ArmJunoDxe: simplify ACPI table installation

Having a three way conditional with callbacks would make sense if the
callbacks weren't (a) identical and (b) didn't return TRUE all the
time. So get rid of the kludge.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>