spl: mmc: Rename spl_boot_mode() to spl_mmc_boot_mode()

The function's name is misleading as one might think it is used
generally to select the boot-mode when in reality it is only used by the
MMC driver to find out in what way it should try reading U-Boot Proper
from a device (either using a filesystem, a raw sector/partition, or an
eMMC boot partition).

Rename it to spl_mmc_boot_mode() to make it more obvious what this
function is about.

Link: https://lists.denx.de/pipermail/u-boot/2020-April/405979.html
Signed-off-by: Harald Seiler <hws@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c
index a2ea363..fb8ad5d 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -298,7 +298,7 @@
 }
 #endif
 
-u32 __weak spl_boot_mode(const u32 boot_device)
+u32 __weak spl_mmc_boot_mode(const u32 boot_device)
 {
 #if defined(CONFIG_SPL_FS_FAT) || defined(CONFIG_SPL_FS_EXT4)
 	return MMCSD_MODE_FS;
@@ -350,7 +350,7 @@
 		}
 	}
 
-	boot_mode = spl_boot_mode(bootdev->boot_device);
+	boot_mode = spl_mmc_boot_mode(bootdev->boot_device);
 	err = -EINVAL;
 	switch (boot_mode) {
 	case MMCSD_MODE_EMMCBOOT: