sunxi: Correct select's of SPL_STACK_R and SPL_SYS_MALLOC_SIMPLE

On ARCH_SUNXI we've been selecting these targets for a long time if
SUPPORT_SPL is set.  However, Lichee Pi Zero is the first platform we've
added that does support SPL but does not build SPL and has exposed a
latent bug.  Both of these symbols depend on SPL not SUPPORT_SPL, so we
need to update our select here otherwise we get a Kconfig warning.

Fixes: f02abb06 ("sunxi: add support for Lichee Pi Zero")
Signed-off-by: Tom Rini <trini@konsulko.com>