Support 16/32 bit color depth

Mado currently uses 32-bit bpp, supporting display devices on
desktop/laptop computers, while Raspberry Pi devices use 16-bit
bpp. To improve mado’s compatibility across various Linux
framebuffer environments, testing showed that
tx->fb_var.bits_per_pixel automatically sets the appropriate bpp
without requiring manual configuration.

backend/fbdev.c

@@ -99,7 +99,6 @@ static bool twin_fbdev_apply_config(twin_fbdev_t *tx)
     /* Set the virtual screen size to be the same as the physical screen */
     tx->fb_var.xres_virtual = tx->fb_var.xres;
     tx->fb_var.yres_virtual = tx->fb_var.yres;
-    tx->fb_var.bits_per_pixel = 32;
     if (ioctl(tx->fb_fd, FBIOPUT_VSCREENINFO, &tx->fb_var) < 0) {
         log_error("Failed to set framebuffer mode");
         return false;
@@ -111,12 +110,6 @@ static bool twin_fbdev_apply_config(twin_fbdev_t *tx)
         return false;
     }
 
-    /* Check bits per pixel */
-    if (tx->fb_var.bits_per_pixel != 32) {
-        log_error("Failed to set framebuffer bpp to 32");
-        return false;
-    }
-
     /* Read unchangable information of the framebuffer */
     ioctl(tx->fb_fd, FBIOGET_FSCREENINFO, &tx->fb_fix);