The multiplier is already promoted to unsigned long, however the
frequency calculations done when using level indexing mode doesn't
use the multiplier computed. It instead hardcodes the multiplier
value of 1000 at all the usage sites.

Clean that up by assigning the multiplier value of 1000 when using
the perf level indexing mode and update the frequency calculations to
use the multiplier instead. It should fix the possible frequency
truncation for all the values greater than or equal to 4GHz on 64-bit
machines.

Fixes: 31c7c139 ("firmware: arm_scmi: Add v3.2 perf level indexing mode support")
Reported-by: Sibi Sankar <quic_sibis@quicinc.com>
Closes: https://lore.kernel.org/all/20231129065748.19871-3-quic_sibis@quicinc.com/
Cc: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20231130204343.503076-2-sudeep.holla@arm.comReviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>