add 'flash list', rewrite 'flash banks'

Rename the existing 'flash banks' implementation as 'flash list', and
replace the broken 'flash_banks' TCL wrapper with a new command handler.

Adds documentation for the new 'flash list' command in the user guide.

src/flash/startup.tcl

@@ -1,16 +1,2 @@
 # Defines basic Tcl procs for OpenOCD flash module
 
-# Show flash in human readable form
-# This is an example of a human readable form of a low level fn
-proc flash_banks {} {
-	set i 0
-	set result ""
-	foreach {a} [ocd_flash banks] {
-		if {$i > 0} {
-			set result "$result\n"
-		}
-		set result [format "$result#%d: %s at 0x%08x, size 0x%08x, buswidth %d, chipwidth %d" $i $a(name) $a(base) $a(size) $a(bus_width) $a(chip_width)]
-		set i [expr $i+1]
-	}
-	return $result
-}