fat_fs: Add support for the "win" variable alignment in FATFS struct

This is to support Sypnosys Designware SDMMC controller read and write
operation where the buffer address is needed to be 16bytes and 512bytes
aligned. Adding macro FS_FATFS_WINDOW_ALIGNMENT to align the "win"
variable address in FATFS struct.

Signed-off-by: Boon Khai Ng <boon.khai.ng@intel.com>

Author: ngboonkhai

subsys/fs/Kconfig.fatfs

@@ -129,6 +129,19 @@ config FS_FATFS_MAX_SS
 	range 512 4096
 	default 512
 
+config FS_FATFS_WINDOW_ALIGNMENT
+	int "Memory alignment for the member \"win\" in FATFS"
+	default 1
+	help
+	  Specifies alignment, in bytes of FAT FS window buffer that is
+	  used for device's read/write operations. MMC controllers may
+	  require read/write buffer to start at memory address with
+	  specific alignment, for example 16 or 512 bytes, the value
+	  provided here is used as such alignment. Note that the window
+	  buffer is internal element of FATFS structure, which means
+	  that, in worst scenario, value provided here may cause FATFS
+	  structure to have size of twice the value
+
 endmenu
 
 endif # FAT_FILESYSTEM_ELM