tests/pc8: don't work around the eDP I2C bug

tests/pc8: don't work around the eDP I2C bug

On the current Kernels, i2c operations on disabled eDP panels don't
work because we don't enable the panel before doing the i2c
transactions. Whenever we try these transactions we print an error
message on dmesg and fail. The current test suite was trying to work
around this problem: we count how many eDP outputs we have and add
them to the final result.

Daniel asked me to not work around the bug, so now the i2c test will
fail until we actually fix the Kernel bug (or stop using eDP panels).

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>