riscv: Generate FDT at runtime for Guest/VM

We generate FDT at runtime for RISC-V Guest/VM so that KVMTOOL users
don't have to pass FDT separately via command-line parameters.

Also, we provide "--dump-dtb <filename>" command-line option to dump
generated FDT into a file for debugging purpose.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Link: https://lore.kernel.org/r/20211119124515.89439-7-anup.patel@wdc.com


Signed-off-by: Will Deacon <will@kernel.org>