cortex-r4: add __rt_ffs
cortex-r4: wrap asm functions with .asmfunc/.endasmfunc
rm48x50: add cache_{enable, disable}
RM48 does not have cache implemented
rm48x50: rt_interrupt_nest should be `volatile rt_uint8_t`
Merge pull request #109 from grissiom/rm48x50

Rm48x50