[MIPS] Replace board_timer_setup function pointer by plat_timer_setup.

Documentation/mips/time.README

arch/mips/au1000/common/setup.c

arch/mips/au1000/common/time.c

arch/mips/basler/excite/excite_setup.c

arch/mips/cobalt/setup.c

arch/mips/ddb5xxx/ddb5477/setup.c

arch/mips/dec/setup.c

arch/mips/dec/time.c

arch/mips/emma2rh/markeins/setup.c

arch/mips/gt64120/wrppmc/setup.c

arch/mips/gt64120/wrppmc/time.c

arch/mips/ite-boards/generic/it8172_setup.c

arch/mips/ite-boards/generic/time.c

arch/mips/jazz/setup.c

arch/mips/jmr3927/rbhma3100/setup.c

arch/mips/kernel/smtc.c

arch/mips/kernel/time.c

arch/mips/lasat/setup.c

arch/mips/mips-boards/atlas/atlas_setup.c

arch/mips/mips-boards/generic/time.c