prom_getenv
ethaddr_str = prom_getenv("ethaddr");
memsize_str = prom_getenv("memsize");
dec_sysid = simple_strtoul(prom_getenv("systype"),
extern char *prom_getenv(char *envname);
extern char *prom_getenv(char *);
const char *prom_getenv(const char *name);
cdev = prom_getenv("console_dev");
ctype = prom_getenv("console");
baud = prom_getenv("lbaud");
baud = prom_getenv("rbaud");
envstr = prom_getenv("board");