powerpc: Fix 32-bit SMP build

powerpc: Fix 32-bit SMP build

Commit 69e3cea8d5fd526 ("powerpc/smp: Make start_secondary_resume
available to all CPU variants") introduced start_secondary_resume to
misc_32.S, however it uses a 64-bit instruction which is not valid on
32-bit platforms.  Use 'stw' instead.

Reported-by: Richard Cochran <[email protected]>
Tested-by: Richard Cochran <[email protected]>
Signed-off-by: Josh Boyer <[email protected]>
Signed-off-by: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>