[MIPS] MT: Improved multithreading support.

arch/mips/Kconfig

arch/mips/kernel/Makefile

arch/mips/kernel/asm-offsets.c

arch/mips/kernel/entry.S

arch/mips/kernel/gdb-low.S

arch/mips/kernel/gdb-stub.c

arch/mips/kernel/genex.S

arch/mips/kernel/head.S

arch/mips/kernel/i8259.c

arch/mips/kernel/irq-msc01.c

arch/mips/kernel/irq.c

arch/mips/kernel/mips-mt.c

arch/mips/kernel/process.c

arch/mips/kernel/ptrace.c

arch/mips/kernel/ptrace32.c

arch/mips/kernel/r4k_switch.S

arch/mips/kernel/smp-mt.c

arch/mips/kernel/smp.c

arch/mips/kernel/smtc-asm.S

arch/mips/kernel/smtc-proc.c