cr50: improve straps reading debug information
cr50: improve straps reading debug information

This patch makes it clear what state each of the straps is in, the
information is printed on the console at startup time.

BRANCH=none
BUG=chrome-os-partner:59833

TEST=tried the new code on the dev board, observed the following in
     the console output at startup:

      strap pin readings: a1:3 a9:1 a6:1 a12:3

    which is consistent with expectations give the dev board
    schematics and mode of operation.

Change-Id: Ie7b2511e0da84b8c9e3462d3f88365e6f2227bfe
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/434938
Reviewed-by: Mary Ruthven <81380f3403fed74252e92df3ed012a1819ec6296@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec