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>

arch/powerpc/platforms/powernv/opal-rtc.c

@@ -34,7 +34,7 @@ static void opal_to_tm(u32 y_m_d, u64 h_m_s_ms, struct rtc_time *tm)
 	tm->tm_wday     = -1;
 }
 
-unsigned long __init opal_get_boot_time(void)
+time64_t __init opal_get_boot_time(void)
 {
 	struct rtc_time tm;
 	u32 y_m_d;
@@ -61,8 +61,7 @@ unsigned long __init opal_get_boot_time(void)
 	y_m_d = be32_to_cpu(__y_m_d);
 	h_m_s_ms = be64_to_cpu(__h_m_s_ms);
 	opal_to_tm(y_m_d, h_m_s_ms, &tm);
-	return mktime(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
-		      tm.tm_hour, tm.tm_min, tm.tm_sec);
+	return rtc_tm_to_time64(&tm);
 }
 
 static __init int opal_time_init(void)