drm/panfrost: Show stored feature registers

Re-reading the feature registers for the sake of displaying the raw
values seems pointless, and in fact showing the copies that we've
already read and stored is arguably more useful in terms of giving
exposure to any potential bugs in that part of the process.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/ce5e414adb008baeed9e2ceb9c88f28d5c74ea42.1556195258.git.robin.murphy@arm.com