drivers: mtd: add Microchip PIC32 internal non-CFI flash driver.

PIC32 internal flash devices are parallel NOR flash divided into
number of banks to allow erase-programming in one while fetch and
execution continues on other. As the flash banks are memory mapped
stored code can be executed directly from flash (XIP), also there
is additional hardware logic to prefetch and cache contents to
improve execution performance. These flash can also be used to
store user data (like environment).
Flash erase and programming are handled by on-chip NVM controller.

Driver implemented driver model but MTD is not really support.

Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Reviewed-by: Simon Glass <sjg@chromium.org>