ARM: 5903/1: arm/perfevents: add support for ARMv7

Adds the Performance Events support for ARMv7 processor, using
the PMNC unit in HW.

Supports the following:
- Cortex-A8 and Cortex-A9 processors,
- dynamic detection of the number of available counters,
   based on the PMCR value,
- runtime detection of the CPU arch (v6 or v7)
   and model (Cortex-A8 or Cortex-A9)

Tested on OMAP3 (Cortex-A8) only.

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