CH32V003 vs. PicoRVD

[burgrp]

PicoRVD is a nice programmer/debugger for CH32V003.
The GDB stub expects flash section to start 0x0, otherwise it is not able to write the data to flash memory.
riscv64-unknown-elf-gcc linker script uses address 0x0.
Solution is to link image with flash starting at 0x instead of 0x8000000.

[burgrp]

Fixed in PR 618.