lcd: make lcd_drawchars() independant of lcd_base

lcd_logo() has the following return value:

 #if defined(CONFIG_LCD_LOGO) && !defined(CONFIG_LCD_INFO_BELOW_LOGO)
	return (void *)((ulong)lcd_base + BMP_LOGO_HEIGHT * lcd_line_length);
 #else
	return (void *)lcd_base;
 #endif

This return value gets assigned to lcd_console_address.
lcd_console_address is not assigned or modified anywhere else.
Thus:

 #if defined(CONFIG_LCD_LOGO) && !defined(CONFIG_LCD_INFO_BELOW_LOGO):
	y' = BMP_LOGO_HEIGHT + y;
	lcd_base + y' * lcd_line_length ==
	lcd_base + (BMP_LOGO_HEIGHT + y) * lcd_line_length ==
	lcd_base + BMP_LOGO_HEIGHT * lcd_line_length + y * lcd_line_length ==
	lcd_console_address + y * lcd_line_length
 #else
	lcd_base + y * lcd_line_length == lcd_console_address + y * lcd_line_length
 #endif

This is a preparatory step for extracting lcd console code into its own
file.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Simon Glass <sjg@chromium.org>