ARM: tegra: timer: Separate clocksource and sched_clock

tegra_clocksource_read should not use cnt32_to_63, wrapping is
already handled in the clocksource code.  Move the cnt32_to_63
into the sched_clock function, and replace the use of clocksource
mult and shift with a multiplication by 1000 to convert us to ns.

Acked-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Tested-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>