[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/arch/i386/interface/pcbios/vesafb.c

 	/* Select mode */
 	if ( ( mode_number = vesafb_select_mode ( mode_numbers, config->width,
 						  config->height,
-						  config->bpp ) ) < 0 ) {
+						  config->depth ) ) < 0 ) {
 		rc = mode_number;
 		goto err_select_mode;
 	}

src/hci/commands/console_cmd.c

 		      struct console_options, config.width, parse_integer ),
 	OPTION_DESC ( "y", 'y', required_argument,
 		      struct console_options, config.height, parse_integer ),
-	OPTION_DESC ( "bpp", 'b', required_argument,
-		      struct console_options, config.bpp, parse_integer ),
+	OPTION_DESC ( "depth", 'd', required_argument,
+		      struct console_options, config.depth, parse_integer ),
 	OPTION_DESC ( "picture", 'p', required_argument,
 		      struct console_options, picture, parse_string ),
 	OPTION_DESC ( "keep", 'k', no_argument,

src/include/ipxe/console.h

 	/** Height */
 	unsigned int height;
 	/** Colour depth */
-	unsigned int bpp;
+	unsigned int depth;
 	/** Left margin */
 	unsigned int left;
 	/** Right margin */