arm64: Kconfig: select KASAN_VMALLOC if KANSAN_GENERIC is enabled

arm64: Kconfig: select KASAN_VMALLOC if KANSAN_GENERIC is enabled

Before this patch, someone who wants to use VMAP_STACK when
KASAN_GENERIC enabled must explicitly select KASAN_VMALLOC.

>From Will's suggestion [1]:
  > I would _really_ like to move to VMAP stack unconditionally, and
  > that would effectively force KASAN_VMALLOC to be set if KASAN is in use

Because VMAP_STACK now depends on either HW_TAGS or KASAN_VMALLOC if
KASAN enabled, in order to make VMAP_STACK selected unconditionally,
we bind KANSAN_GENERIC and KASAN_VMALLOC together.

Note that SW_TAGS supports neither VMAP_STACK nor KASAN_VMALLOC now,
so this is the first step to make VMAP_STACK selected unconditionally.

Bind KANSAN_GENERIC and KASAN_VMALLOC together is supposed to cost more
memory at runtime, thus the alternative is using SW_TAGS KASAN instead.

[1]: https://lore.kernel.org/lkml/20210204150100.GE20815@willie-the-truck/

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Link: https://lore.kernel.org/r/20210324040522.15548-6-lecopzer.chen@mediatek.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>