sunxi: Remove some unnecessary #ifdefs

We always define CONFIG_MISC_INIT_R on sunxi and misc_init_r is never
called in the spl, so the linker will optimize it and parse_spl_header(),
of which it is the only caller, away.

On the tests I've done (Orange Pi PC build) the SPL actually becomes
8 bytes smaller with this patch.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>