drm/i915: Fix conversion between clock ticks and nanoseconds

drm/i915: Fix conversion between clock ticks and nanoseconds

When tick values are large, the multiplication by NSEC_PER_SEC is larger
than 64 bits and results in bad conversions.

The issue is seen in PMU busyness counters that look like they have
wrapped around due to bad conversion. i915 PMU implementation returns
monotonically increasing counters. If a count is lesser than previous
one, it will only return the larger value until the smaller value
catches up. The user will see this as zero delta between two
measurements even though the engines are busy.

Fix it by using mul_u64_u32_div()

Fixes: 77cdd054dd2c ("drm/i915/pmu: Connect engine busyness stats from GuC to pmu")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14955
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://lore.kernel.org/r/20251016000350.1152382-2-umesh.nerlige.ramappa@intel.com
(cherry picked from commit 2ada9cb1df3f5405a01d013b708b1b0914efccfe)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo: Added the Fixes tag while cherry-picking to fixes]