riscv: Fix config KASAN && DEBUG_VIRTUAL

__virt_to_phys function is called very early in the boot process (ie
kasan_early_init) so it should not be instrumented by KASAN otherwise it
bugs.

Fix this by declaring phys_addr.c as non-kasan instrumentable.

Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Fixes: 8ad8b727

 (riscv: Add KASAN support)
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>