arm64: Calculate size for idmap_pg_dir at compile time

arm64: Calculate size for idmap_pg_dir at compile time

Now that we can calculate the number of levels required for
mapping a va width, reserve exact number of pages that would
be required to cover the idmap. The idmap should be able to handle
the maximum physical address size supported.

Cc: Will Deacon <[email protected]>
Signed-off-by: Suzuki K. Poulose <[email protected]>
Reviewed-by: Ard Biesheuvel <[email protected]>
Tested-by: Ard Biesheuvel <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>