Add McSPI support to device tree

[hansemro]

Resources:

• https://github.com/hansemro/kernel_omap_otter-common/blob/84763bbf0a9138cb0ba7b42411cd8d0405c1c684/arch/arm/mach-omap2/board-4430kc1-tablet-panel.c#L114-L138
• SPI device: https://github.com/hansemro/kernel_omap_otter-common/blob/2cae8a87e7e2ef6f20bce00e6fe806bb45b6c683/drivers/video/backlight/o2micro_bl.c

Required for bringing up backlight IC for LCD panel (which is the only SPI device used on the kindle).

[hansemro]

McSPI is already accessible normally (without device tree changes), so I will close this issue in favor of this issue: #11