ACPI: APMT: Fix kerneldoc and indentation

Add missing kerneldoc and fix alignment on one of the arguments of
apmt_add_platform_device function.

Signed-off-by: Besar Wicaksono <bwicaksono@nvidia.com>
Link: https://lore.kernel.org/r/20221111234323.16182-1-bwicaksono@nvidia.com


[will: Fixed up additional indentation issue]
Signed-off-by: Will Deacon <will@kernel.org>