xtensa: hw_breakpoint: include header for missing prototype

Add the prototype for restore_dbreak() to <asm/hw_breakpoint.h> and use
that header in hw_breakpoint.c to prevent a build warning:

arch/xtensa/kernel/hw_breakpoint.c:263:6: warning: no previous prototype for 'restore_dbreak' [-Wmissing-prototypes]
263 | void restore_dbreak(void)

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Chris Zankel <[e-mail]>
Cc: Max Filippov <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Max Filippov <[e-mail]>

arch/xtensa/include/asm/hw_breakpoint.h

···
 void hw_breakpoint_pmu_read(struct perf_event *bp);
 int check_hw_breakpoint(struct pt_regs *regs);
 void clear_ptrace_hw_breakpoint(struct task_struct *tsk);
+void restore_dbreak(void);
 
 #else
 

arch/xtensa/kernel/hw_breakpoint.c

···
 #include <linux/percpu.h>
 #include <linux/perf_event.h>
 #include <asm/core.h>
+#include <asm/hw_breakpoint.h>
 
 /* Breakpoint currently in use for each IBREAKA. */
 static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[XCHAL_NUM_IBREAK]);