powerpc/ptrace: move ptrace_triggered() into hw_breakpoint.c

ptrace_triggered() is declared in asm/hw_breakpoint.h and
only needed when CONFIG_HW_BREAKPOINT is set, so move it
into hw_breakpoint.c

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8402c516023da1371953a65af7df2008758ea0c4.1582848567.git.christophe.leroy@c-s.fr