pstore/ramoops: Add ramoops.mem_name= command line option

pstore/ramoops: Add ramoops.mem_name= command line option

Add a method to find a region specified by reserve_mem=nn:align:name for
ramoops. Adding a kernel command line parameter:

  reserve_mem=12M:4096:oops ramoops.mem_name=oops

Will use the size and location defined by the memmap parameter where it
finds the memory and labels it "oops". The "oops" in the ramoops option
is used to search for it.

This allows for arbitrary RAM to be used for ramoops if it is known that
the memory is not cleared on kernel crashes or soft reboots.

Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20240613155527.591647061@goodmis.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>