LoongArch: Add LBT extensions support

Loongson Binary Translation (LBT) is used to accelerate binary translation,
which contains 4 sketch (scratch) registers (scr0 to scr3), x86/ARM eflags
(eflags) and x87 fpu stack pointer (ftop).

This patch support kernel to save/restore these registers, handle the LBT
exception and maintain sigcontext.

Signed-off-by: Qi Hu <huqi@loongson.cn>

Author: specialpointcentral

arch/loongarch/Kconfig

@@ -545,6 +545,15 @@ config CPU_HAS_LASX
 
 	  If unsure, say Y.
 
+config CPU_HAS_LBT
+	bool "Support for Loongson Binary Translation"
+	help
+	  Loongson Binary Translation (LBT) introduces 4 sketch registers (SCR0 to SCR3),
+	  x86/ARM eflags (eflags) and x87 fpu stack pointer (ftop).
+	  When this option is enabled, the kernel will support allocation and switching
+	  LBT related registers.
+	  If you want to use this feature or Loongson Architecture Translator (LAT), say Y.
+
 config CPU_HAS_PREFETCH
 	bool
 	default y

arch/loongarch/include/asm/asm-prototypes.h

@@ -2,6 +2,7 @@
 #include <linux/uaccess.h>
 #include <asm/checksum.h>
 #include <asm/fpu.h>
+#include <asm/lbt.h>
 #include <asm/mmu_context.h>
 #include <asm/page.h>
 #include <asm/ftrace.h>