powerpc/opcodes: Add shorter macros for registers for use with PPC_RAW_xx()

Today we have __REG_Rx macros . They are mainly meant for
internal use by macros __PPC_RA() and friends macros which
allows uses like __PPC_RA(R12).

When used with PPC_RAW_xx() macros, it gives a result which is
not very readable.

Add shorter macros _Rx in order to improve readability when
used with PPC_RAW_xx() macros.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ec34d92b7c2f810622261acfeeed4b0a0f4d01bd.1621506159.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/ppc-opcode.h

@@ -76,6 +76,40 @@
 #define	__REGA0_R30	30
 #define	__REGA0_R31	31
 
+/* For use with PPC_RAW_() macros */
+#define	_R0	0
+#define	_R1	1
+#define	_R2	2
+#define	_R3	3
+#define	_R4	4
+#define	_R5	5
+#define	_R6	6
+#define	_R7	7
+#define	_R8	8
+#define	_R9	9
+#define	_R10	10
+#define	_R11	11
+#define	_R12	12
+#define	_R13	13
+#define	_R14	14
+#define	_R15	15
+#define	_R16	16
+#define	_R17	17
+#define	_R18	18
+#define	_R19	19
+#define	_R20	20
+#define	_R21	21
+#define	_R22	22
+#define	_R23	23
+#define	_R24	24
+#define	_R25	25
+#define	_R26	26
+#define	_R27	27
+#define	_R28	28
+#define	_R29	29
+#define	_R30	30
+#define	_R31	31
+
 #define IMM_L(i)               ((uintptr_t)(i) & 0xffff)
 #define IMM_DS(i)              ((uintptr_t)(i) & 0xfffc)
 #define IMM_DQ(i)              ((uintptr_t)(i) & 0xfff0)