drm: enable (most) W=1 warnings by default across the subsystem

drm: enable (most) W=1 warnings by default across the subsystem

At least the i915 and amd drivers enable a bunch more compiler warnings
than the kernel defaults.

Extend most of the W=1 warnings to the entire drm subsystem by
default. Use the copy-pasted warnings from scripts/Makefile.extrawarn
with s/KBUILD_CFLAGS/subdir-ccflags-y/ to make it easier to compare and
keep up with them in the future.

This is similar to the approach currently used in i915.

Some of the -Wextra warnings do need to be disabled, just like in
Makefile.extrawarn, but take care to not disable them for W=2 or W=3
builds, depending on the warning.

There are too many -Wformat-truncation warnings to cleanly fix up front;
leave that warning disabled for now.

v3:
- Drop -Wmissing-declarations (already enabled by default)
- Drop -Wmissing-prototypes (already enabled by default)

v2:
- Drop -Wformat-truncation (too many warnings)
- Drop -Wstringop-overflow (already enabled by default)

Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Christian König <[email protected]>
Cc: Pan
Cc: Karol Herbst <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Rob Clark <[email protected]>
Cc: Abhinav Kumar <[email protected]>
Cc: Dmitry Baryshkov <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: Marijn Suijten <[email protected]>
Cc: Hamza Mahfooz <[email protected]>
Acked-by: Javier Martinez Canillas <[email protected]>
Acked-by: Thomas Zimmermann <[email protected]>
Acked-by: Sui Jingfeng <[email protected]>
Acked-by: Danilo Krummrich <[email protected]>
Acked-by: Maxime Ripard <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/a50f1a69d5af72e913996179a75bc3a71d81ebea.1709629403.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <[email protected]>