arch: arm64: librem5_defconfig: Enable BT_HCIUART_BCM
Following the comment [1] let's enable BT_HCIUART_BCM to support btattach instead of the depcreated hciattach.
1: librem5-base#76 (comment 281624)
Signed-off-by: Alistair Francis alistair@alistair23.me