mtd: map.h endian fix

Need to use endian neutral functions to read/write LE h/w registers. I.e
insted of __raw_readl and _raw_writel, readl_relaxed and writel_relaxed. If
the first just read/write register with memory barrier, the second will
byteswap it if host operates in BE mode.

Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>