[RFC v5 22/26] powerpc: Adopt nvram module for PPC64

Adopt nvram module to reduce code duplication. The IOC_NVRAM_GET_OFFSET ioctl as implemented on PPC64 validates the offset returned by pmac_get_partition(). Add this test to the nvram module. Note that the old PPC32 generic_nvram module lacked this test. So when CONFIG_PPC32 && CONFIG_PPC_PMAC,

[RFC v5 22/26] powerpc: Adopt nvram module for PPC64

Adopt nvram module to reduce code duplication. The IOC_NVRAM_GET_OFFSET ioctl as implemented on PPC64 validates the offset returned by pmac_get_partition(). Add this test to the nvram module. Note that the old PPC32 generic_nvram module lacked this test. So when CONFIG_PPC32 CONFIG_PPC_PMAC,