picolisp/src/pico.h: This patch does two things.

1. Conditionally add function prototypes for
   target/platform specific picolisp functions.

2. Change mkStr's argument to const char* instead
   of just char *.
Add platform_picolisp.h for the avr32 platform.
Conditionally include references to target specific
picoLisp functions.

All references come from platform_picolisp.h (which
should be added for all targets).
mkStr(): The argument to this function is now a
const char* instead of just char*.
avr32/lcd.c: Include picoLisp support for the following functions:

* lcd_prinl
* lcd_getpos
* lcd_buttons
* lcd_cursor
* lcd_display

Note: Only lcd_definechar remains.