UPSTREAM: nvmem: core: remove regmap dependency

UPSTREAM: nvmem: core: remove regmap dependency

nvmem uses regmap_raw_read/write apis to read/write data from providers,
regmap raw apis stopped working with recent kernels which removed raw
accessors on mmio bus. This resulted in broken nvmem for providers
which are based on regmap mmio bus. This issue can be fixed temporarly
by moving to other regmap apis, but we might hit same issue in future.
Moving to interfaces based on read/write callbacks from providers would
be more robust.

This patch removes regmap dependency from nvmem and introduces
read/write callbacks from the providers.

Without this patch nvmem providers like qfprom based on regmap mmio
bus would not work.

Change-Id: I510034b1cfe3057ef1e7eb20ad6a4175458f0b2b
Reported-by: Rajendra Nayak <rjendra@qti.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Finley Xiao <finley.xiao@rock-chips.com>
cherry pick from 795ddd18d38f9762fbfefceab9aa16caef0cf431)