py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for. A
port will also provide mphalport.h with further HAL declarations.
If VT100 support is not available then a given implementation of
mp_hal_erase_line_from_cursor might need to know the number of characters
to erase.
This patch does not change generated code when VT100 is supported, since
compiler can optimise away the argument.
stijn