cfi_cmdset_0001: factorize code to wait for flash status

This allows for much better abstraction and separation of the XIP and
non-XIP cases with their own specific implementations.  This fixes the
case where a timeout was tripped on in the XIP case by the code that
was meant for the non-XIP case only.

This also makes for a nice code reduction.
Signed-off-by: Nicolas Pitre <nico@cam.org>
CC: "Alexey, Korolev" <alexey.korolev@intel.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>