powerpc: use time64_t in read_persistent_clock

Looking through the remaining users of the deprecated mktime()
function, I found the powerpc rtc handlers, which use it in
place of rtc_tm_to_time64().

To clean this up, I'm changing over the read_persistent_clock()
function to the read_persistent_clock64() variant, and change
all the platform specific handlers along with it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index ffe7c71..a47de82 100644
--- a/arch/powerpc/include/asm/machdep.h
+++ b/arch/powerpc/include/asm/machdep.h
@@ -83,7 +83,7 @@
 
 	int		(*set_rtc_time)(struct rtc_time *);
 	void		(*get_rtc_time)(struct rtc_time *);
-	unsigned long	(*get_boot_time)(void);
+	time64_t	(*get_boot_time)(void);
 	unsigned char 	(*rtc_read_val)(int addr);
 	void		(*rtc_write_val)(int addr, unsigned char val);