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>
diff --git a/drivers/bootcount/bootcount_env.c b/drivers/bootcount/bootcount_env.c
index ec5f942..c3618d3 100644
--- a/drivers/bootcount/bootcount_env.c
+++ b/drivers/bootcount/bootcount_env.c
@@ -10,7 +10,7 @@
 
 void bootcount_store(ulong a)
 {
-	int upgrade_available = getenv_ulong("upgrade_available", 10, 0);
+	int upgrade_available = env_get_ulong("upgrade_available", 10, 0);
 
 	if (upgrade_available) {
 		env_set_ulong("bootcount", a);
@@ -20,11 +20,11 @@
 
 ulong bootcount_load(void)
 {
-	int upgrade_available = getenv_ulong("upgrade_available", 10, 0);
+	int upgrade_available = env_get_ulong("upgrade_available", 10, 0);
 	ulong val = 0;
 
 	if (upgrade_available)
-		val = getenv_ulong("bootcount", 10, 0);
+		val = env_get_ulong("bootcount", 10, 0);
 
 	return val;
 }