scripts/Makefile.lib: EFI: Use capsule CRT instead of ESL file

The EFI Capsule ESL file (EFI Signature List File) used for authentication
is a binary generated from the EFI Capsule public key certificate. Instead
of including it in the source repo, automatically generate it from the
certificate file during the build process.

Currently, sandbox is the only device using this, so removed its ESL file
and set the (new) CONFIG_EFI_CAPSULE_CRT_FILE config to point to its public
key certificate.

Signed-off-by: Jonathan Humphreys <j-humphreys@ti.com>
diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index ee71f41..2fb24d7 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -298,13 +298,15 @@
 	  Select the max capsule index value used for capsule report
 	  variables. This value is used to create CapsuleMax variable.
 
-config EFI_CAPSULE_ESL_FILE
-	string "Path to the EFI Signature List File"
+config EFI_CAPSULE_CRT_FILE
+	string "Path to the EFI capsule public key certificate"
 	depends on EFI_CAPSULE_AUTHENTICATE
 	help
-	  Provides the path to the EFI Signature List file which will
-	  be embedded in the platform's device tree and used for
-	  capsule authentication at the time of capsule update.
+	  Provides the path to the EFI capsule public key certificate that
+	  corresponds to the capsule signing key. This certificate will be used
+	  to generate the EFI capsule ESL (signature list file) that gets
+	  embedded in the platform's device tree and used for capsule
+	  authentication at the time of capsule update.
 
 config EFI_DEVICE_PATH_TO_TEXT
 	bool "Device path to text protocol"