powerpc/64s: Add missing declaration for machine_check_early_boot()

There's no declaration for machine_check_early_boot(), which leads to a
build failure with W=1. Add one.

Fixes: 2f5182cf ("powerpc/64s: early boot machine check handler")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221125132521.2167039-1-mpe@ellerman.id.au

arch/powerpc/include/asm/interrupt.h

@@ -602,6 +602,7 @@ ____##func(struct pt_regs *regs)
 /* kernel/traps.c */
 DECLARE_INTERRUPT_HANDLER_NMI(system_reset_exception);
 #ifdef CONFIG_PPC_BOOK3S_64
+DECLARE_INTERRUPT_HANDLER_RAW(machine_check_early_boot);
 DECLARE_INTERRUPT_HANDLER_ASYNC(machine_check_exception_async);
 #endif
 DECLARE_INTERRUPT_HANDLER_NMI(machine_check_exception);