flashrom_tester: Change the wp_toggle semantics

wp_toggle and wp_range had some confusing behaviour where enabling wp
would set a range, but disabling wp would not unset the range
(explicitly).  This was a way to workaround the MTD kernel driver
semantics. Now make things very explicit, enabling software write
protect will set the range to the whole chip. Disabling write protect
will set the range to 0,0. This makes all drivers behave the same as
MTD, and documents the exact behaviour explicitly.

BUG=b:244663741
BRANCH=None
TEST=flashrom_tester --libflashrom host # MTD and non-MTD
TEST=flashrom_tester --flashrom_binary # MTD and non-MTD

Change-Id: Ia01d612d988e6580a7c5f0fd448ccc319ce9b181
Signed-off-by: Evan Benn <evanbenn@chromium.org>
---
M util/flashrom_tester/flashrom/src/cmd.rs
M util/flashrom_tester/flashrom/src/flashromlib.rs
M util/flashrom_tester/flashrom/src/lib.rs
3 files changed, 37 insertions(+), 25 deletions(-)