annotate Attributes argument for SetVariable() when possible

[yeggor]

Mostly we see such code where op_enum() does not help, because operand is not an immediate value:

mov r9d, X      ; DataSize
lea r8d, [r9+Y] ; Attributes (X + Y)

However, it will work when we encounter:

mov r8d, X      ; Attributes

In such cases we will get:

gRT->SetVariable(L"CheckUserPSW", &VendorGuid, VARIABLE_ATTRIBUTE_NV_BS_RT, DataSize, &Data);

instead of:

gRT->SetVariable(L"CheckUserPSW", &VendorGuid, 7u, DataSize, &Data);

Related PR: #99