[ulib][kvstore] Avoid use of C99 features

Makes it easier to pull this code into bootloaders

Change-Id: I3414c94b47ba08ae950499ebb92c2e68ecb96325

[ulib][kvstore] include crc32

Change-Id: If79d48c13ab723b827fc087119b7cdfc50635330

[ulib][kvstore] simple binary small key/value storage container

Provide a container for storage of small (less than 256 byte)
key/value pairs, intended for passing configuration/version state
between bootloaders and running systems (at least initially) via
the sys-config partition or other transports.

Change-Id: I8c8159eb6199e93816d843fdbbb2fb374e002d77