tracing: Remove PPC32 wart from config TRACING_SUPPORT

config TRACING_SUPPORT has an exception for PPC32, because PPC32
didn't have irqflags tracing support.

But that hasn't been true since commit 5d38902c ("powerpc: Add
irqtrace support for 32-bit powerpc") (Jun 2009).

So remove the exception for PPC32 and the comment.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>