mb/emulation/*-riscv: Remove "UCB" from RISC-V board names

RISC-V is not a project of the University of California, Berkeley,
anymore; it stands on its own feet now.

Remove the "UCB" component from the RISC-V mainboards in the "emulation"
directory, and don't set MAINBOARD_VENDOR to UCB, either.

Change-Id: I301d9d0091a714e62375052e5af06a9197876688
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/28951
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/emulation/qemu-riscv/Kconfig.name

@@ -1,2 +1,2 @@
-config BOARD_EMULATION_QEMU_UCB_RISCV
-	bool "QEMU ucb riscv"
+config BOARD_EMULATION_QEMU_RISCV
+	bool "QEMU riscv"