ARM: orion: implement ARM delay timer

Implement an ARM delay timer to be used for udelay() on orion legacy
platforms.  This allows us to skip the delay loop calibration at boot.

It also means that udelay() will be unaffected by CPU frequency changes
when cpufreq is enabled on these platforms.

Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>