configs/beaglev_defconfig: new defconfig

This commit introduces support for the RISC-V based BeagleV platform,
which uses a Starfive JH7100.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
[yann.morin.1998@free.fr: use:  eval $(make printvars)]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>