mmc: block: Support the fixed index for mmcblk with aliases nodes

mmc: block: Support the fixed index for mmcblk with aliases nodes

Now, index of mmcblk is allocated in accordance with probing time.
If want to use the mmcblk1 for some device, it can use alias.

aliases {
	mmc0 = &mmc0;	/* mmcblk0 for eMMC */
	mmc1 = &mmc2;	/* mmcblk1 for SD */
	mmc2 = &mmc1;	/* mmcblk2 for SDIO*/
};

If there are no corresponding values, it might be allocated with
existing scheme.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
[sw0312.kim: port to v4.14
 - apply to host index instead of name_idx because host index is used in this version
]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I44673d62e546ea0aeedd9cac314dbfd31fdcce66