emummc: Add boot entry emuMMC selection

Using the key `emupath` on a boot entry will load the selected emuMMC.
This can also be forced by using the correct boot cfg storage bit and writing the path at the emummc path offset. Check readme for these.

This can only be used if the emuMMC was created via Nyx. because of the raw_based and file_based files that have emuMMC info.
(emupath=emuMMC/RAW1, emupath=emuMMC/SD00, etc)

bootloader/utils/types.h

@@ -55,6 +55,7 @@ typedef int bool;
 #define BOOT_CFG_AUTOBOOT_EN (1 << 0)
 #define BOOT_CFG_FROM_LAUNCH (1 << 1)
 #define BOOT_CFG_FROM_ID     (1 << 2)
+#define BOOT_CFG_TO_EMUMMC   (1 << 3)
 #define BOOT_CFG_SEPT_RUN    (1 << 7)
 
 #define EXTRA_CFG_KEYS    (1 << 0)
@@ -75,6 +76,7 @@ typedef struct __attribute__((__packed__)) _boot_cfg_t
 		struct
 		{
 			char id[8];
+			char emummc_path[0x78];
 		};
 		u8 xt_str[0x80];
 	};