On KASAN + 16K_PAGES + 48BIT_VA
 arch/arm64/mm/kasan_init.c: In function ‘kasan_early_init’:
 include/linux/compiler.h:484:38: error: call to ‘__compiletime_assert_95’ declared with attribute error: BUILD_BUG_ON failed: !IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE)
    _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

Currently KASAN will not work on 16K_PAGES and 48BIT_VA, so
forbid such configuration to avoid above build failure.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Suzuki K. Poulose <Suzuki.Poulose@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>