shim: Initial support for KVM_SET_GSI_ROUTING

[softickllc]

in shim/include/kvm_irq_routing.h : many nested structures and unions added, which will be actually available when other ioctl implementations from other branches are merged together.
Just for completeness they have been declared in the same file.
These shall be removed later.

[codecov]

Codecov Report

Merging #122 (ffdbbd7) into irqchip (2ec8738) will not change coverage.
The diff coverage is 100.00%.

❗ Current head ffdbbd7 differs from pull request most recent head edf6cb6. Consider uploading reports for the commit edf6cb6 to get more accurate results

@@            Coverage Diff            @@
##           irqchip      #122   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          210       210           
  Lines         6922      6924    +2     
  Branches       156       156           
=========================================
+ Hits          6922      6924    +2     

Impacted Files	Coverage Δ
shim/src/handle_vm_kvm_set_gsi_routing.c	100.00% <100.00%> (ø)
...m/tests/src/test_handle_vm_kvm_set_gsi_routing.cpp	100.00% <100.00%> (ø)
shim/src/handle_vm_kvm_irqfd.c	100.00% <0.00%> (ø)
shim/tests/src/test_handle_vm_kvm_irqfd.cpp	100.00% <0.00%> (ø)