disk: dos: add code for creating MBR partition layout

Add a code for creating and writing MBR partition layout. The code generates
similar layout of EBRs (Exteneded Block Records) and logical volumes as
Linux's fdisk utility.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
diff --git a/disk/part_dos.h b/disk/part_dos.h
index dd909a9..5055822 100644
--- a/disk/part_dos.h
+++ b/disk/part_dos.h
@@ -19,6 +19,8 @@
 #define DOS_PART_TYPE_EXTENDED_LBA	0x0F
 #define DOS_PART_TYPE_EXTENDED_LINUX	0x85
 
+#define DOS_PART_DEFAULT_GAP		2048
+
 typedef struct dos_partition {
 	unsigned char boot_ind;		/* 0x80 - active			*/
 	unsigned char head;		/* starting head			*/