Add two macros which generate functions to extract the relevent bits
from event->attr.config{,1,2}.

EVENT_DEFINE_RANGE() defines an accessor for a range of bits in the
event, as well as a "max" function that gives the maximum value of the
field based on the bit width.

EVENT_DEFINE_RANGE_FORMAT() defines the accessor & max routine and also
a format attribute for use in the PMU's attr_groups.
Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
[mpe: move to powerpc, ugly but descriptive macro names]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>