ARM: 6195/1: OMAP3: pmu: make CPU_HAS_PMU dependent on OMAP3_EMU

CPU performance event counters on v7 cores will only operate
if either the NIDEN or DBGEN signals are driven high.

For the OMAP3 platform, these signals are driven low by default
but DBGEN can be asserted by selecting the OMAP3_EMU Kconfig option,
which enables the virtual clock for hardware debugging peripherals.

Acked-by: Jean Pihet <jpihet@mvista.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>