x86: ich-spi: Convert driver to spi-mem ops

With the introduction of the new spi-mem model operations changed
slightly. The new spi-mem operations make things a bit easier to
handle for ich-spi flash interface. This patch converts the ich-spi
driver by using spi-mem operations.

Signed-off-by: Bernhard Messerklinger <bernhard.messerklinger@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

Tested on Intel CrownBay and MinnowMax
Tested-by: Bin Meng <bmeng.cn@gmail.com>

[bmeng: fix compiler warnings when building the driver for 64-bit]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>