riscv: Fix DEBUG_VIRTUAL false warnings

KERN_VIRT_SIZE used to encompass the kernel mapping before it was
redefined when moving the kasan mapping next to the kernel mapping to only
match the maximum amount of physical memory.

Then, kernel mapping addresses that go through __virt_to_phys are now
declared as wrong which is not true, one can use __virt_to_phys on such
addresses.

Fix this by redefining the condition that matches wrong addresses.

Fixes: f7ae0233 ("riscv: Move KASAN mapping next to the kernel mapping")
Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>