MIPS: add definitions for Loongson-specific CP0.Diag1 register

This 32-bit CP0 register is named GSCause in Loongson manuals. It carries
Loongson extended exception information. We name it Diag1 because we
fear the "GSCause" name might get changed in the future.

Reviewed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: WANG Xuerui <git@xen0n.name>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: xen0n

arch/mips/include/asm/mipsregs.h

@@ -86,6 +86,7 @@
 #define CP0_XCONTEXT $20
 #define CP0_FRAMEMASK $21
 #define CP0_DIAGNOSTIC $22
+#define CP0_DIAGNOSTIC1 $22, 1
 #define CP0_DEBUG $23
 #define CP0_DEPC $24
 #define CP0_PERFORMANCE $25
@@ -1051,6 +1052,13 @@
 /* Flush FTLB */
 #define LOONGSON_DIAG_FTLB	(_ULCAST_(1) << 13)
 
+/*
+ * Diag1 (GSCause in Loongson-speak) fields
+ */
+/* Loongson-specific exception code (GSExcCode) */
+#define LOONGSON_DIAG1_EXCCODE_SHIFT	2
+#define LOONGSON_DIAG1_EXCCODE		GENMASK(6, 2)
+
 /* CvmCtl register field definitions */
 #define CVMCTL_IPPCI_SHIFT	7
 #define CVMCTL_IPPCI		(_U64CAST_(0x7) << CVMCTL_IPPCI_SHIFT)