Currently we access individual bytes of an option vector via
ldub_phys() to test for the presence of a particular capability
within that byte. Currently this is only done for the "dynamic
reconfiguration memory" capability bit. If that bit is present,
we pass a boolean value to spapr_h_cas_compose_response()
to generate a modified device tree segment with the additional
properties required to enable this functionality.

As more capability bits are added, will would need to modify the
code to add additional option vector accesses and extend the
param list for spapr_h_cas_compose_response() to include similar
boolean values for these parameters.

Avoid this by switching to spapr_ovec_* helpers so we can do all
the parsing in one shot and then test for these additional bits
within spapr_h_cas_compose_response() directly.

Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NBharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

PAPR guests advertise their capabilities to the platform by passing
an ibm,architecture-vec structure via an
ibm,client-architecture-support hcall as described by LoPAPR v11,
B.6.2.3. during early boot.

Using this information, the platform enables the capabilities it
supports, then encodes a subset of those enabled capabilities (the
5th option vector of the ibm,architecture-vec structure passed to
ibm,client-architecture-support) into the guest device tree via
"/chosen/ibm,architecture-vec-5".

The logical format of these these option vectors is a bit-vector,
where individual bits are addressed/documented based on the byte-wise
offset from the beginning of the bit-vector, followed by the bit-wise
index starting from the byte-wise offset. Thus the bits of each of
these bytes are stored in reverse order. Additionally, the first
byte of each option vector is encodes the length of the option vector,
so byte offsets begin at 1, and bit offset at 0.

This is not very intuitive for the purposes of mapping these bits to
a particular documented capability, so this patch introduces a set
of abstractions that encapsulate the work of parsing/encoding these
options vectors and testing for individual capabilities.

Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
[dwg: Tweaked double-include protection to not trigger a checkpatch
 false positive]
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>