[RFC v6 07/25] char/nvram: Allow the set_checksum and initialize ioctls to be omitted

The drivers/char/nvram module has previously only supported RTC "CMOS" NVRAM, for which it provides appropriate checksum ioctls. Make these ioctls optional so the module can be re-used with other kinds of NVRAM. The ops struct methods that implement the ioctls now return error codes so that a

[RFC v6 07/25] char/nvram: Allow the set_checksum and initialize ioctls to be omitted

The drivers/char/nvram module has previously only supported RTC CMOS NVRAM, for which it provides appropriate checksum ioctls. Make these ioctls optional so the module can be re-used with other kinds of NVRAM. The ops struct methods that implement the ioctls now return error codes so that a