Patch from Deepak Saxena

One of the problems I have seen with several bootloaders is
that they forget to disable network devices before jumping 
into the kernel and we end up with kernel text being overwritten
by random data before the in-kernel driver resets the devices.
This patch adds a blurb to the ARM Bootloader documentation 
reminding developers to quiesce all DMA capable devices before
executing the kernel.

Signed-off-by: Deepak Saxena
Signed-off-by: Russell King