sparc64: Fix prototype warnings in hibernate.c

sparc64: Fix prototype warnings in hibernate.c

Fix the following warnings:
arch/sparc/power/hibernate.c:22:5: warning: no previous prototype for ‘pfn_is_nosave’
arch/sparc/power/hibernate.c:30:6: warning: no previous prototype for ‘save_processor_state’
arch/sparc/power/hibernate.c:35:6: warning: no previous prototype for ‘restore_processor_state’

The prototypes are available from linux/suspend.h so include that.

Link: https://lore.kernel.org/r/20240710094155.458731-5-andreas@gaisler.com
Signed-off-by: Andreas Larsson <andreas@gaisler.com>