max32660: put slave-only code in `#ifdef`s
max32660: put slave-only code in `#ifdef`s

This fixes a bunch of "<method> defined but not used" build warnings
when working with a board that only uses the I2C master and not the
slave.

Also fixed various checkpatch.pl errors and warnings that appeared in
the lines that were moved.

BRANCH=none
BUG=chromium:1008568
TEST=Build a MAX32660 board that only uses the I2C master and check that
     it succeeds with no warnings. Modify it to use the slave as well
     and check that host commands still work.

Change-Id: Icee04ad6d7b641f934e56b670be8770710a41e64
Signed-off-by: Harry Cutts <1d9acf085666736c25fb5139ba37ad9d917ae7f5@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1832892
Reviewed-by: Jes Klinke <d7a45737f2d52b53995e6ff74608c5989a9d5d52@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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