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/drivers/pci/fsl_pci_init.c b/drivers/pci/fsl_pci_init.c
index af20cf0..df76a94 100644
--- a/drivers/pci/fsl_pci_init.c
+++ b/drivers/pci/fsl_pci_init.c
@@ -390,7 +390,7 @@
 
 #ifdef CONFIG_SRIO_PCIE_BOOT_MASTER
 	/* boot from PCIE --master */
-	char *s = getenv("bootmaster");
+	char *s = env_get("bootmaster");
 	char pcie[6];
 	sprintf(pcie, "PCIE%d", pci_info->pci_num);
 
@@ -673,7 +673,7 @@
 #ifdef CONFIG_SRIO_PCIE_BOOT_MASTER
 	} else {
 		/* boot from PCIE --master releases slave's core 0 */
-		char *s = getenv("bootmaster");
+		char *s = env_get("bootmaster");
 		char pcie[6];
 		sprintf(pcie, "PCIE%d", pci_info->pci_num);