drm/i915: Remove memory frequency calculation

This memory frequency calculated is only used to check if it is zero,
what is not useful as it will never actually be zero.

Also the calculation is wrong, we should be checking other bit to
select the appropriate frequency multiplier while this code is stuck
with a fixed multiplier.

So here dropping it as whole.

v2:
- Also remove memory frequency calculation for gen9 LP platforms

Cc: Yakui Zhao <yakui.zhao@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Fixes: 5d0c938e

 ("drm/i915/gen11+: Only load DRAM information from pcode")
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211013010046.91858-1-jose.souza@intel.com