tools/lib/atusb.c: added SRAM access to atusb driver
tools/lib/atusb.c: added SRAM access to atusb driver

- atusb.c (atusb_sram_write, atusb_sram_read): SRAM access functions
- atusb.c (atusb_driver): added new functions to driver operations

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan