powerpc/time: Avoid using get_tbl() and get_tbu() internally

get_tbl() is confusing as it returns the content of TBL register
on PPC32 but the concatenation of TBL and TBU on PPC64.

Use mftb() instead.

Do the same with get_tbu() for consistency allthough it's name
is less confusing.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/41573406a4eab98838decaa91649086fef1e6119.1601556145.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/delay.h

@@ -54,7 +54,7 @@ extern void udelay(unsigned long usecs);
 ({                                                                             \
 	typeof(condition) __ret;                                               \
 	unsigned long __loops = tb_ticks_per_usec * timeout;                   \
-	unsigned long __start = get_tbl();                                     \
+	unsigned long __start = mftb();                                     \
                                                                                \
 	if (delay) {                                                           \
 		while (!(__ret = (condition)) &&                               \

arch/powerpc/include/asm/time.h

@@ -76,9 +76,9 @@ static inline u64 get_tb(void)
 	unsigned int tbhi, tblo, tbhi2;
 
 	do {
-		tbhi = get_tbu();
-		tblo = get_tbl();
-		tbhi2 = get_tbu();
+		tbhi = mftbu();
+		tblo = mftb();
+		tbhi2 = mftbu();
 	} while (tbhi != tbhi2);
 
 	return ((u64)tbhi << 32) | tblo;
@@ -123,7 +123,7 @@ static inline void set_dec(u64 val)
 
 static inline unsigned long tb_ticks_since(unsigned long tstamp)
 {
-	return get_tbl() - tstamp;
+	return mftb() - tstamp;
 }
 
 #define mulhwu(x,y) \

arch/powerpc/kernel/time.c

@@ -448,8 +448,8 @@ void __delay(unsigned long loops)
 		 */
 		spin_cpu_relax();
 	} else {
-		start = get_tbl();
-		while (get_tbl() - start < loops)
+		start = mftb();
+		while (mftb() - start < loops)
 			spin_cpu_relax();
 	}
 	spin_end();