[AMDGPU] Increase detection range for s_mov, v_cmpx transformation.

We found that it might be beneficial to have the SIOptimizeExecMasking
pass detect more cases where v_cmp, s_and_saveexec patterns can be
transformed to s_mov, v_cmpx patterns. Currently, the search range
for finding a fitting v_cmp instruction is 5, however, this is doubled
to 10 here.

Reviewed By: foad

Differential Revision: https://reviews.llvm.org/D123367