lib/logic_iomem: correct fallback config references

Due to some renaming, we ended up with the "indirect iomem"
naming in Kconfig, following INDIRECT_PIO. However, clearly
I missed following through on that in the ifdefs, but so far
INDIRECT_IOMEM_FALLBACK isn't used by any architecture.

Reported-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Fixes: ca2e3342 ("lib: add iomem emulation (logic_iomem)")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>