drm/msm: Fix spelling mistake "Purgable" -> "Purgeable"

There is a spelling mistake in debugfs gem stats. Fix it. Also
re-align output to cater for the extra 1 character.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210406133939.425987-1-colin.king@canonical.com


Signed-off-by: Rob Clark <robdclark@chromium.org>