powerpc/kernel: Combine vec/loc for STD_EXCEPTION_PSERIES

The STD_EXCEPTION_PSERIES macro takes both a vector number, and a
location (memory address). However both are always identical, so combine
them to save repeating ourselves.

This does mean an exception handler must always exist at the location in
memory that matches its vector number. But that's OK because this is the
"STD" macro (standard), which does exactly that. We have other macros
for the other cases, eg. STD_EXCEPTION_PSERIES_OOL (out of line).

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>