[InlineSpiller] Relax re-materialization restriction for statepoint

We should be careful to allow count of re-materialization of operands to be less
then number of physical registers.

STATEPOINT instruction has a variable number of operands and potentially very big.
So re-materialization for all operands is disabled at the moment if restrict-statepoint-remat is true.

The patch relaxes the re-materialization restriction for STATEPOINT instruction allowing it for
fixed operands. Specifically it is about call target.

Reviewers: reames
Reviewed By: reames
Subscribers: llvm-commits, qcolombet, hiraditya
Differential Revision: https://reviews.llvm.org/D75335