Documentation: Spell vboot all lowercase

Update all occurrences of vboot and spell it lowercase.

Change-Id: I432b0db8a3dda43b71844e557a3d89180f25f1c3
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39799
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

Documentation/releases/coreboot-4.11-relnotes.md

@@ -175,7 +175,7 @@ of becoming more generally useful.
 Payload integration has been updated, coreinfo learned to cope with
 UPPER CASE commands and libpayload knows how to deal with USB3 hubs.
 
-### Added VBOOT support to the following platforms:
+### Added vboot support to the following platforms:
 
 * intel/gm45
 * intel/nehalem

Documentation/releases/coreboot-4.5-relnotes.md

@@ -73,7 +73,7 @@ Areas with significant updates
 
 ### Vendorcode
 * AMD (14 commits) - Cleanup, add libagesa.a builds, remove unused code.
-* Google (22 commits) - VBoot2 updates and cleanup
+* Google (22 commits) - vboot2 updates and cleanup
 * Intel (86 commits) - Add Intel FSP 2.0, update Broadwell DE support
 
 ### Payloads (37 commits)

Documentation/releases/coreboot-4.6-relnotes.md

@@ -180,7 +180,7 @@ SuperIO (12 commits)
 * Add 2 new chips
 * Consolidate code to use common routines
 
-Vboot (23 commits)
+vboot (23 commits)
 * Add support for recovery hash space in TPM
 
 RISC-V (25 commits)

Documentation/releases/coreboot-4.8.1-relnotes.md

@@ -77,7 +77,7 @@ Security
 --------
 * Start of refactoring the TPM software stack
 * Introduced coreboot security section in kconfig
-* VBoot & TPM code moved into src/security
+* vboot & TPM code moved into src/security
 
 Intelmetool
 -----------