[cmdline] Rename "console" command's --bpp option to --depth

Rename the "--bpp" option to "--depth", to free up the single-letter
option "-b" for "--bottom" in preparation for adding margin support.

This does not break backwards compatibility with documented features,
since the "console" command has not yet been documented.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/console.h

@@ -27,7 +27,7 @@ struct console_configuration {
 	/** Height */
 	unsigned int height;
 	/** Colour depth */
-	unsigned int bpp;
+	unsigned int depth;
 	/** Left margin */
 	unsigned int left;
 	/** Right margin */