intel: drop redundant `packed` attribute

../include/drm/i915_drm.h:2233:1: warning: packed attribute is unnecessary for 'i915_context_engines_load_balance' [-Werror=packed]
 } __attribute__((packed));
 ^
../include/drm/i915_drm.h:2271:1: warning: packed attribute is unnecessary for 'i915_context_engines_bond' [-Werror=packed]
 } __attribute__((packed));
 ^
../include/drm/i915_drm.h:2399:1: warning: packed attribute is unnecessary for 'i915_context_engines_parallel_submit' [-Werror=packed]
 } __attribute__((packed));
 ^
../include/drm/i915_drm.h:2473:1: warning: packed attribute is unnecessary for 'i915_context_param_engines' [-Werror=packed]
 } __attribute__((packed));
 ^