Rename some CPU_MIPSxxx options and add new CPU_MIPSxxx options

[Sgalabov_gmail.com]

Summary

This revision does the following renames:
CPU_MIPS24KC -> CPU_MIPS24K
CPU_MIPS74KC -> CPU_MIPS74K
CPU_MIPS1004KC -> CPU_MIPS1004K

It also adds the following new CPU_MIPSxxx options:
CPU_MIPS24KE, CPU_MIPS34K, CPU_MIPS1074K, CPU_INTERAPTIV, CPU_PROAPTIV

CPU_MIPSxxxxKC is limiting and possibly misleading as it implies the MIPSxxxxK CPU has no FPU.
It would be better if the CPUs are named after their standard functionalities only and the presence or absence of FPU can then be controlled via the CPU_HAVEFPU option.

I will send out another dependent revision that moves MIPS 32 r2 and r3 CPUs to use the EHB instruction for clearing hazards instead of NOP/SSNOP.

[Sgalabov_gmail.com]

After discussion with imp@, removed the CPU_MIPS24KE option, as 24KE is not really different than 24K, apart from having DSP ASE, which can be detected dynamically via Config3 register.

[adrian]

This fine by me; it reminds me that we never started using the mips24k pieces for those atheros SoC cores (all the ar71xx, ar91xx, ar933x, etc) that are actually mips24k. They're mips4k.

We can fix that later though!

[Sgalabov_gmail.com]

I meant to talk to you about possibly moving the Atheros SoCs to MIPS24K, but then got distracted with other things :-)
Yeah, I guess we can move the SoCs later. I did that for the Ralink SoCs in sys/mips/ralink for now, will be using the new cpu options with the Ralink/Mediatek FDT stuff too.