Make crossystem.h more polite and more useful.

This adds a VB_MAX_STRING_PROPERTY for callers that don't
want to guess at how big to make their buffers.

Additionally, it changes the size parameter to VbGetPropertyString()
from int to size_t.

BUG=None
TEST=compile the code
BRANCH=none

Change-Id: I22809d48e13b535593cb22a56444e2dcb27791a5
Reviewed-on: https://chromium-review.googlesource.com/175039
Reviewed-by: Randall Spangler <[email protected]>
Tested-by: Richard Barnette <[email protected]>
Reviewed-by: Bill Richardson <[email protected]>
Commit-Queue: Richard Barnette <[email protected]>
6 files changed