fix(boot_time): Update boot time doc

Fix measurement values for filesystem (end of kernel to user space
readiness).
Add link to SPL Falcon mode so user can refer either SBL or SPL flow
based on the requirement.
SBL flow requires used to specify bootargs in kernel unlike SPL flow
where bootargs could be passed to kernel. Add a note for same in doc.

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

Author: paresh-bhagat12

source/linux/How_to_Guides/Target/How_to_boot_quickly.rst

@@ -97,6 +97,10 @@ This section describes an overview of the modifications that can be done to achi
 .. Image:: /images/optimized_bootflow_sbl_mpu.png
      :align: center
 
+.. note::
+
+   This document focuses on optimized boot flow using Secondary Boot Loader (SBL). Users can also achieve shorter boot time by using Secondary Program Loader (SPL) flow. Refer doc :ref:`U-Boot Falcon Mode <U-Boot-Falcon-Mode>`.
+
 Reducing bootloader time
 ------------------------
 
@@ -242,6 +246,10 @@ Secondary Boot Loader (SBL)
         .. Image:: /images/SBL_singlerank_ddr.png
          :align: center
 
+.. note::
+
+   SBL flow requires specifying kernel bootargs in either the Linux defconfig or device tree, otherwise the Linux image will fail to boot.
+
 Reducing Linux kernel boot time
 -------------------------------
 
@@ -611,9 +619,9 @@ To measure the instance when the filesystem starts, navigate to :file:`init/main
     +-----------------+-----------+
     |  Linux Kernel   |    530    |
     +-----------------+-----------+
-    |     Tiny FS     |    188    |
+    |     Tiny FS     |    190    |
     +-----------------+-----------+
-    |           Total |    964    |
+    |      Total      |    966    |
     +-----------------+-----------+
 
 Bootloader loads HSM binary (9KB), MCU/DSP image (50KB) and Kernel+FS image (22MB) in the above measurements