[DAGCombine][MSP430] use shift amount threshold in DAGCombine (2/2)

Continuation of:
D69116

Contributes to a fix for PR43559:
https://bugs.llvm.org/show_bug.cgi?id=43559

See also D69099 and D69116

Use the TLI hook in DAGCombine.cpp to guard against creating
shift nodes that are not optimal for a target.

Patch by: @joanlluch (Joan LLuch)

Differential Revision: https://reviews.llvm.org/D69120