drm/xe/pf: Drop rounddown_pow_of_two fair LMEM limitation

This effectively reverts commit 4c3fe5ea ("drm/xe/pf: Limit
fair VF LMEM provisioning") since we don't need it any more after
non-contig VRAM allocations were fixed. This allows larger LMEM
auto-provisioning for VFs, so instead:

 [ ] GT0: PF: LMEM available(14096M) fair(1 x 8192M)
 [ ] GT0: PF: VF1 provisioned with 8589934592 (8.00 GiB) LMEM
or
 [ ] GT0: PF: LMEM available(14096M) fair(2 x 4096M)
 [ ] GT0: PF: VF1..VF2 provisioned with 4294967296 (4.00 GiB) LMEM

we may get:

 [ ] GT0: PF: LMEM available(14096M) fair(1 x 14096M)
 [ ] GT0: PF: VF1 provisioned with 14780727296 (13.8 GiB) LMEM
and
 [ ] GT0: PF: LMEM available(14096M) fair(2 x 7048M)
 [ ] GT0: PF: VF1..VF2 provisioned with 7390363648 (6.88 GiB) LMEM

Fixes: 1e32ffbc ("drm/xe/sriov: support non-contig VRAM provisioning")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20250910222439.32869-1-michal.wajdeczko@intel.com