[RFC v6 08/25] char/nvram: Implement NVRAM read/write methods

Refactor the RTC "CMOS" NVRAM functions so that they can be used as arch_nvram_ops methods. Checksumming logic is moved from the misc device operations to the nvram read/write operations. This makes the misc device implementation more generic. This also preserves the locking semantics such that

[RFC v6 08/25] char/nvram: Implement NVRAM read/write methods

Refactor the RTC CMOS NVRAM functions so that they can be used as arch_nvram_ops methods. Checksumming logic is moved from the misc device operations to the nvram read/write operations. This makes the misc device implementation more generic. This also preserves the locking semantics such that