arm64: Mandate VMAP_STACK

arm64: Mandate VMAP_STACK

On arm64, VMAP_STACK has been enabled by default for a while now, and
the only reason to disable it was a historical lack of support for
KASAN_VMALLOC. Today there's no good reason to disable VMAP_STACK.

Mandate VMAP_STACK, which will allow code to be simplified in
subsequent patches.

Suggested-by: Will Deacon <will@kernel.org>
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-v1-1-8de98ca0f91c@debian.org
Signed-off-by: Will Deacon <will@kernel.org>