configs: Explicitly specify vendor and mainboard

Relying on the implicit defaults for these settings can cause issues in
the future. For example, commit 8cc4c5a1e76c0c8aee3a14618c15d38e3bd2bd61
(config.dell_optiplex_9010_sff: Specify board model) was done to prevent
a build failure when adding support for other Dell mainboards which make
the default board change.

Change-Id: Ie0da6254def8b38e9fb053fc7d530dfb46760861
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56079
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/configs/config.libretrend_lt1000 b/configs/config.libretrend_lt1000
index 33159f1..0d4f543 100644
--- a/configs/config.libretrend_lt1000
+++ b/configs/config.libretrend_lt1000
@@ -1,4 +1,5 @@
 CONFIG_VENDOR_LIBRETREND=y
+CONFIG_BOARD_LIBRETREND_LT1000=y
 CONFIG_POWER_STATE_OFF_AFTER_FAILURE=y
 CONFIG_GENERIC_LINEAR_FRAMEBUFFER=y
 CONFIG_TPM2=y