Documentation: embargoed-hardware-issues.rst: Add myself for RISC-V

I'm not sure exactly how RISC-V fits into the story here, but I'm happy
to voluteer a sort of catch-all for vendors who aren't otherwise
represented.

Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/20230912180657.31841-1-palmer@rivosinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: palmer-dabbelt

Documentation/process/embargoed-hardware-issues.rst

@@ -251,6 +251,7 @@ an involved disclosed party. The current ambassadors list:
   IBM Z		Christian Borntraeger <borntraeger@de.ibm.com>
   Intel		Tony Luck <tony.luck@intel.com>
   Qualcomm	Trilok Soni <tsoni@codeaurora.org>
+  RISC-V	Palmer Dabbelt <palmer@dabbelt.com>
   Samsung	Javier González <javier.gonz@samsung.com>
 
   Microsoft	James Morris <jamorris@linux.microsoft.com>