arm: omap: specify PMUs are for ARMv7 CPUs

Now that we can specify which PMU variant we're likely to deal with, do
so in the omap board code. This will allow us to split the ARMv6, ARMv7,
and XScale PMU drivers.

The unnecessary include of asm/pmu.h is also removed.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Olof Johansson <olof@lixom.net>
Signed-off-by: Olof Johansson <olof@lixom.net>