arm64: remove CONFIG_VMAP_STACK conditionals from traps overflow stack

With VMAP_STACK now always enabled on arm64, remove the
CONFIG_VMAP_STACK checks from overflow stack definitions and related
code in arch/arm64/kernel/traps.c. The overflow_stack and
panic_bad_stack() logic are now unconditionally included, simplifying
the source and matching the mandatory stack model.

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20250707-arm64_vmap-v1-5-8de98ca0f91c@debian.org
Signed-off-by: Will Deacon <will@kernel.org>

Author: leitao

arch/arm64/kernel/traps.c

@@ -894,8 +894,6 @@ void bad_el0_sync(struct pt_regs *regs, int reason, unsigned long esr)
 			      "Bad EL0 synchronous exception");
 }
 
-#ifdef CONFIG_VMAP_STACK
-
 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
 	__aligned(16);
 
@@ -927,7 +925,6 @@ void __noreturn panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigne
 	nmi_panic(NULL, "kernel stack overflow");
 	cpu_park_loop();
 }
-#endif
 
 void __noreturn arm64_serror_panic(struct pt_regs *regs, unsigned long esr)
 {