recipes: Update LICENSE variable to use SPDX license identifiers

Fix QA warnings:
WARNING: efitools-1.9.2+gitAUTOINC+392836a46c-r0 do_package_qa: QA Issue: Recipe LICENSE includes obsolete licenses GPLv2 [obsolete-license]
WARNING: mokutil-0.3.0+gitAUTOINC+e19adc575c-r0 do_package_qa: QA Issue: Recipe LICENSE includes obsolete licenses GPLv3 [obsolete-license]

This is the result of automated script conversion:
poky/scripts/contrib/convert-spdx-licenses.py meta-secure-core

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>

meta-tpm/recipes-tpm/openssl-tpm-engine/openssl-tpm-engine_0.5.0.bb

@@ -2,7 +2,7 @@ DESCRIPTION = "OpenSSL secure engine based on TPM hardware"
 HOMEPAGE = "https://github.com/mgerstner/openssl_tpm_engine"
 SECTION = "security/tpm"
 
-LICENSE = "openssl"
+LICENSE = "OpenSSL"
 LIC_FILES_CHKSUM = "file://LICENSE;md5=11f0ee3af475c85b907426e285c9bb52"
 
 DEPENDS += "openssl trousers"

meta-tpm/recipes-tpm/pcr-extend/pcr-extend_git.bb

@@ -1,7 +1,7 @@
 SUMMARY = "Command line utility to extend hash of arbitrary data into a TPMs PCR."
 SECTION = "security/tpm"
 
-LICENSE = "GPLv2"
+LICENSE = "GPL-2.0-only"
 LIC_FILES_CHKSUM = "file://COPYING;md5=b234ee4d69f5fce4486a80fdaf4a4263"
 
 DEPENDS = "libtspi"

meta-tpm/recipes-tpm/tss-testsuite/tss-testsuite_git.bb

@@ -10,7 +10,7 @@ using the TPM. \
 HOMEPAGE = "${SOURCEFORGE_MIRROR}/projects/trousers"
 SECTION = "security/tpm"
 
-LICENSE = "GPLv2"
+LICENSE = "GPL-2.0-only"
 LIC_FILES_CHKSUM = "file://LICENSE;md5=751419260aa954499f7abaabaa882bbe"
 
 DEPENDS = "trousers"