doc: board: ti: k3: image alt texts

Provide alternative texts for images.

Fixes: 6e8fa0611f19 ("board: ti: k3: Convert boot flow ascii flow to svg")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
diff --git a/doc/board/ti/k3.rst b/doc/board/ti/k3.rst
index f4576c5..5be8fa2 100644
--- a/doc/board/ti/k3.rst
+++ b/doc/board/ti/k3.rst
@@ -47,6 +47,7 @@
 to after it has finished loading everything into internal SRAM.
 
 .. image:: img/boot_flow_01.svg
+  :alt: Boot flow up to wakeup domain SPL
 
 The wakeup SPL, running on a wakeup domain core, will initialize DDR and
 any peripherals needed load the larger binaries inside the `tispl.bin`
@@ -56,6 +57,7 @@
 OP-TEE and the main domain's U-Boot SPL.
 
 .. image:: img/boot_flow_02.svg
+  :alt: Boot flow up to main domain SPL
 
 The main domain's SPL, running on a 64bit application core, has
 virtually unlimited space (billions of bytes now that DDR is working) to
@@ -64,6 +66,7 @@
 finally prepare the main domain to run Linux.
 
 .. image:: img/boot_flow_03.svg
+  :alt: Complete boot flow up to Linux
 
 This is the typical boot flow for all K3 based SoCs, however this flow
 offers quite a lot in the terms of flexibility, especially on High