openpower: Add loadkeys package to enable backtab

This is a copy of the buildroot package 'kbd', but with a custom install
command that only installs the 'loadkeys' binary, saving almost 1MB of
space.

The loadkeys command then allows us to add additional keymap definitions
during init to enable the use of Shift-Tab on the VGA console.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/garrison_defconfig b/openpower/configs/garrison_defconfig
index eafb6d5..2709965 100644
--- a/openpower/configs/garrison_defconfig
+++ b/openpower/configs/garrison_defconfig
@@ -68,3 +68,4 @@
 BR2_PACKAGE_MDADM=y
 BR2_TARGET_ROOTFS_CPIO_XZ=y
 BR2_TARGET_ROOTFS_INITRAMFS=y
+BR2_PACKAGE_LOADKEYS=y