powerpc/trace/syscalls: Update syscall name matching logic to account for ppc_ prefix

Some syscall entry functions on powerpc are prefixed with
ppc_/ppc32_/ppc64_ rather than the usual sys_/__se_sys prefix. fork(),
clone(), swapcontext() are some examples of syscalls with such entry
points. We need to match against these names when initializing ftrace
syscall tracing.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>