MFC r307943-r307944, r308698

r307943 by andrew:
Remove the need for the delay to be zero when MULTIDELAY is undefined,
it may be useful to only enable this in some configs.

Sponsored by: ABT Systems Ltd

r307944 by andrew:
Add MULTIDELAY support to the am335x dmtimer. This will be useful for
testing Cortex-A8 support in GENERIC.

Sponsored by: ABT Systems Ltd

r308698 by loos:
After r308533, the platform compatible string must be an exact match.

Use "ti,am33xx" instead of "ti,am335x", which gives an exact match in every
DTS we support.

This fixes the boot on TI SoCs after r308533.

Suggested by: gonzo
Sponsored by: Rubicon Communications, LLC (Netgate)