powerpc/rtas: remove ibm_suspend_me_token

There's not a compelling reason to cache the value of the token for
the ibm,suspend-me function. Just look it up when needed in the RTAS
syscall's special case for it.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210408140630.205502-4-nathanl@linux.ibm.com