riscv: add hardware error trap handler support

Add support for handling hardware error traps (exception code 19)
in the RISC-V architecture. The changes include:

- Add do_trap_hardware_error function declaration in asm-prototypes.h
- Add hardware error trap vector entry in entry.S exception vector table
- Implement do_trap_hardware_error handler in traps.c that generates
  SIGBUS with BUS_MCEERR_AR for hardware errors

This enables proper handling of hardware error exceptions that may occur
in RISC-V systems, providing appropriate error reporting and signal
generation for user space processes.

Signed-off-by: Rui Qi <qirui.001@bytedance.com>
Link: https://patch.msgid.link/20260202094200.53735-1-qirui.001@bytedance.com
[pjw@kernel.org: clean up commit message slightly]
Signed-off-by: Paul Walmsley <pjw@kernel.org>

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

@@ -40,6 +40,7 @@ asmlinkage void riscv_v_context_nesting_end(struct pt_regs *regs);
 #define DECLARE_DO_ERROR_INFO(name)	asmlinkage void name(struct pt_regs *regs)
 
 DECLARE_DO_ERROR_INFO(do_trap_unknown);
+DECLARE_DO_ERROR_INFO(do_trap_hardware_error);
 DECLARE_DO_ERROR_INFO(do_trap_insn_misaligned);
 DECLARE_DO_ERROR_INFO(do_trap_insn_fault);
 DECLARE_DO_ERROR_INFO(do_trap_insn_illegal);

arch/riscv/kernel/entry.S

@@ -498,6 +498,7 @@ SYM_DATA_START_LOCAL(excp_vect_table)
 	RISCV_PTR do_trap_unknown /* cause=16 */
 	RISCV_PTR do_trap_unknown /* cause=17 */
 	RISCV_PTR do_trap_software_check /* cause=18 is sw check exception */
+	RISCV_PTR do_trap_hardware_error /* hardware error (19) */
 SYM_DATA_END_LABEL(excp_vect_table, SYM_L_LOCAL, excp_vect_table_end)
 
 #ifndef CONFIG_MMU

arch/riscv/kernel/traps.c

@@ -165,6 +165,8 @@ asmlinkage __visible __trap_section void name(struct pt_regs *regs)		\
 
 DO_ERROR_INFO(do_trap_unknown,
 	SIGILL, ILL_ILLTRP, "unknown exception");
+DO_ERROR_INFO(do_trap_hardware_error,
+	SIGBUS, BUS_MCEERR_AR, "hardware error");
 DO_ERROR_INFO(do_trap_insn_misaligned,
 	SIGBUS, BUS_ADRALN, "instruction address misaligned");
 DO_ERROR_INFO(do_trap_insn_fault,