env: Rename getenv/_f() to env_get()

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

Quite a few places use getenv() in a condition context, provoking a
warning from checkpatch. These are fixed up in this patch also.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/freescale/b4860qds/b4860qds.c b/board/freescale/b4860qds/b4860qds.c
index 83a7015..1fea91b 100644
--- a/board/freescale/b4860qds/b4860qds.c
+++ b/board/freescale/b4860qds/b4860qds.c
@@ -195,7 +195,7 @@
 	      vid, vdd_target/10);
 
 	/* check override variable for overriding VDD */
-	vdd_string = getenv("b4qds_vdd_mv");
+	vdd_string = env_get("b4qds_vdd_mv");
 	if (vdd_override == 0 && vdd_string &&
 	    !strict_strtoul(vdd_string, 10, &vdd_string_override))
 		vdd_override = vdd_string_override;
@@ -542,7 +542,7 @@
 			 * Extract hwconfig from environment since environment
 			 * is not setup properly yet
 			 */
-			getenv_f("hwconfig", buffer, sizeof(buffer));
+			env_get_f("hwconfig", buffer, sizeof(buffer));
 			buf = buffer;
 
 			if (hwconfig_subarg_cmp_f("fsl_b4860_serdes2",