A Sector Map Parameter Table contains a sequence of the following
descriptors:
* (Optional) configuration detection command descriptors, one for
each command to run to determine the current configuration. This
exists only if the flash layout is configurable.
* Sector map descriptors, one for each possible configuration. On
a flash device with a non-configurable layout, there is only one
such descriptor.

Previously we only supported the non-configurable case with a single
descriptor. This commit adds support for multiple configurations.