target-openrisc: remove conflicting definitions from cpu.h

On an ARM host, the registers definitions from cpu.h clash
with /usr/include/sys/ucontext.h. As there are unused, just remove
them.

Cc: Jia Liu <proljc@gmail.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

target-openrisc/cpu.h

@@ -89,24 +89,6 @@ enum {
 /* Interrupt */
 #define NR_IRQS  32
 
-/* Registers */
-enum {
-    R0 = 0, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10,
-    R11, R12, R13, R14, R15, R16, R17, R18, R19, R20,
-    R21, R22, R23, R24, R25, R26, R27, R28, R29, R30,
-    R31
-};
-
-/* Register aliases */
-enum {
-    R_ZERO = R0,
-    R_SP = R1,
-    R_FP = R2,
-    R_LR = R9,
-    R_RV = R11,
-    R_RVH = R12
-};
-
 /* Unit presece register */
 enum {
     UPR_UP = (1 << 0),