linux-imx

Documentation: ARM: List new omap MMC requirements

Earlier the PBIAS regulator was optional, not so with recent
omap_hsmmc changes. To make things easier for people with
custom .config files, let's add minimal documentation for it
as suggested by Russell King <rmk+kernel@arm.linux.org.uk>.

Signed-off-by: Tony Lindgren <tony@atomide.com>