env: Rename getenv_hex(), getenv_yesno(), getenv_ulong()

We are now using an env_ prefix for environment functions. Rename these
for consistency. Also add function comments in common.h.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>

lib/fdtdec.c

@@ -1240,7 +1240,7 @@ int fdtdec_setup(void)
 # endif
 # ifndef CONFIG_SPL_BUILD
 	/* Allow the early environment to override the fdt address */
-	gd->fdt_blob = (void *)getenv_ulong("fdtcontroladdr", 16,
+	gd->fdt_blob = (void *)env_get_ulong("fdtcontroladdr", 16,
 						(uintptr_t)gd->fdt_blob);
 # endif
 #endif