powerpc/kasan: Fix boot failure with RELOCATABLE && FSL_BOOKE

powerpc/kasan: Fix boot failure with RELOCATABLE && FSL_BOOKE

When enabling CONFIG_RELOCATABLE and CONFIG_KASAN on FSL_BOOKE,
the kernel doesn't boot.

relocate_init() requires KASAN early shadow area to be set up because
it needs access to the device tree through generic functions.

Call kasan_early_init() before calling relocate_init()

Reported-by: Lexi Shao <shaolexi@huawei.com>
Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b58426f1664a4b344ff696d18cacf3b3e8962111.1575036985.git.christophe.leroy@c-s.fr