env: Rename SYS_MMC_ENV_PART to ENV_MMC_EMMC_HW_PARTITION

Rename the variable and add ENV_ prefix, so that all configuration
options which are related to environment would have an CONFIG_ENV_
prefix. No functional change.

Use ENV_MMC_EMMC_HW_PARTITION to clarify this is the eMMC hardware
partition selector, not a software partition table entry selector.
Retain the ENV_MMC_ prefix to make it easier to search for all the
SD/MMC related ENV options. Update the help text accordingly.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/env/mmc.c b/env/mmc.c
index dba99bd..5d1cb78 100644
--- a/env/mmc.c
+++ b/env/mmc.c
@@ -157,7 +157,7 @@
 	int hwpart = 0;
 	int err;
 
-#if defined(CONFIG_SYS_MMC_ENV_PART)
+#if defined(CONFIG_ENV_MMC_EMMC_HW_PARTITION)
 	hwpart = mmc_get_env_part(mmc);
 #endif
 
@@ -216,7 +216,7 @@
 	if (!IS_ENABLED(CONFIG_ENV_REDUNDANT))
 		return false;
 
-	if (CONFIG_SYS_MMC_ENV_PART != 1)
+	if (CONFIG_ENV_MMC_EMMC_HW_PARTITION != 1)
 		return false;
 
 	return mmc_offset(mmc, 0) == mmc_offset(mmc, 1);
@@ -239,10 +239,10 @@
 	return 0;
 }
 
-#ifdef CONFIG_SYS_MMC_ENV_PART
+#ifdef CONFIG_ENV_MMC_EMMC_HW_PARTITION
 __weak uint mmc_get_env_part(struct mmc *mmc)
 {
-	return CONFIG_SYS_MMC_ENV_PART;
+	return CONFIG_ENV_MMC_EMMC_HW_PARTITION;
 }
 
 static unsigned char env_mmc_orig_hwpart;