[Targets] Don't automatically include the scheduler class enum from...

[Targets] Don't automatically include the scheduler class enum from *GenInstrInfo.inc with GET_INSTRINFO_ENUM. Make targets request is separately.

Most of the targets don't need the scheduler class enum.

I have an X86 scheduler model change that causes some names in the enum to become about 18000 characters long. This is because using instregex in scheduler models causes the scheduler class to get named with every instruction that matches the regex concatenated together. MSVC has a limit of 4096 characters for an identifier name. Rather than trying to come up with way to reduce the name length, I'm just going to sidestep the problem by not including the enum in X86.

llvm-svn: 320552