mtd: nand: vf610_nfc: Freescale NFC for VF610, MPC5125 and others

This driver supports Freescale NFC (NAND flash controller) found on
Vybrid (VF610), MPC5125, MCF54418 and Kinetis K70. The driver has
been tested using 8-bit and 16-bit NAND interface on the ARM based
Vybrid SoC VF500 and VF610 platform.
parameter page reading.

Limitations:
- Untested on MPC5125 and M54418.
- DMA and pipelining not used.
- 2K pages or less.
- No chip select, one NAND chip per controller.
- No hardware ECC.

Some paths have been hand-optimized and evaluated by measurements
made using mtd_speedtest.ko on a 100MB MTD partition.

Colibri VF50
        eb write     %   eb read     %   page write      %   page read     %
rel/opt     5175           11537                4560             11039
opt         5164 -0.21     11420 -1.01          4737 +3.88       10918 -1.10
none        5113 -1.20     11352 -1.60          4490 -1.54       10865 -1.58

Colibri VF61
        eb write     %   eb read     %   page write      %   page read     %
rel/opt     5766           13096                5459             12846
opt         5883 +2.03     13064 -0.24          5561 +1.87       12802 -0.34
none        5701 -1.13     12980 -0.89          5488 +0.53       12735 -0.86

rel = using readl_relaxed/writel_relaxed in optimized paths
opt = hand-optimized by combining multiple accesses into one read/write

The measurements have not been statistically verfied, hence use them
with care. The author came to the conclusion that using the relaxed
variants of readl/writel are not worth the additional code.

Signed-off-by: Bill Pringlemeir <bpringlemeir@nbsps.com>
Tested-by: Albert ARIBAUD <albert.aribaud@3adev.fr>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>