Enable GKI 2.0 signing

This is to check the interity of a generic boot.img.

Note: build/make/target/product/gsi/testkey_rsa2048.pem is generated by:
      `openssl genrsa -out testkey_rsa2048.pem 2048`.

Bug: 177862434
Test: `make bootimage`
      `unpack_bootimg --boot_img $OUT/boot.img --out unpack`
      `avbtool info_image --image ./unpack/boot_signature`
Change-Id: I12ea4c666f71ad6b6c245d629e41904eb8d90858
diff --git a/target/board/generic_arm64/BoardConfig.mk b/target/board/generic_arm64/BoardConfig.mk
index 30c033d..15c311c 100644
--- a/target/board/generic_arm64/BoardConfig.mk
+++ b/target/board/generic_arm64/BoardConfig.mk
@@ -74,9 +74,13 @@
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 576716800
 
 BOARD_RAMDISK_USE_LZ4 := true
-BOARD_BOOT_HEADER_VERSION := 3
+BOARD_BOOT_HEADER_VERSION := 4
 BOARD_MKBOOTIMG_ARGS += --header_version $(BOARD_BOOT_HEADER_VERSION)
 
+# Enable GKI 2.0 signing.
+BOARD_GKI_SIGNING_KEY_PATH := build/make/target/product/gsi/testkey_rsa2048.pem
+BOARD_GKI_SIGNING_ALGORITHM := SHA256_RSA2048
+
 BOARD_KERNEL_BINARIES := \
     kernel-4.19-gz \
     kernel-5.4 kernel-5.4-gz kernel-5.4-lz4 \
diff --git a/target/product/gsi/testkey_rsa2048.pem b/target/product/gsi/testkey_rsa2048.pem
new file mode 100644
index 0000000..64de31c
--- /dev/null
+++ b/target/product/gsi/testkey_rsa2048.pem
@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----