feat(Snagfactory): Add a note for Fastboot buffer size

Snagfactory flashing will fail if fastboot buffer size is smaller than
the file being flashed for non-sparse images. Add a note for the same.

Signed-off-by: Paresh Bhagat <[email protected]>

Author: paresh-bhagat12

source/linux/Foundational_Components/Tools/Flash_via_Fastboot.rst

@@ -98,6 +98,13 @@ images after make can be found in :file:`board-support/built-images`.
 
 For more details regarding USB DFU refer :ref:`usb-device-firmware-upgrade-label`.
 
+.. note::
+
+   CONFIG_FASTBOOT_BUF_SIZE is defined in am6x_a53_snagfactory.config and specifies
+   the maximum buffer size for flashing files. Its value must be equal or greater
+   than the largest file size being flashed. If smaller, non-sparse images will
+   not flash correctly due to issues with chunked processing.
+
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