samples/bpf: Enable powerpc support

samples/bpf: Enable powerpc support

Add the necessary definitions for building bpf samples on ppc.

Since ppc doesn't store function return address on the stack, modify how
PT_REGS_RET() and PT_REGS_FP() work.

Also, introduce PT_REGS_IP() to access the instruction pointer.

Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Ananth N Mavinakayanahalli <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Naveen N. Rao <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>