Revert "vga: do not resize the screen on hw_invalidate"

This causes ctrl+alt+u or ctrl+alt+f to not work when windows hasn't been
resized first. Other graphic emulators do resize the screen on
hw_invalidate.

This reverts commit 0bd8246.

hw/vga.c

@@ -1852,8 +1852,7 @@ static void vga_update_display(void *opaque)
     if (ds_get_bits_per_pixel(s->ds) == 0) {
         /* nothing to do */
     } else {
-        full_update = s->full_update;
-        s->full_update = 0;
+        full_update = 0;
         if (!(s->ar_index & 0x20)) {
             graphic_mode = GMODE_BLANK;
         } else {
@@ -1883,7 +1882,8 @@ static void vga_invalidate_display(void *opaque)
 {
     VGACommonState *s = opaque;
 
-    s->full_update = 1;
+    s->last_width = -1;
+    s->last_height = -1;
 }
 
 void vga_common_reset(VGACommonState *s)

hw/vga_int.h

@@ -159,7 +159,6 @@ typedef struct VGACommonState {
     uint32_t last_width, last_height; /* in chars or pixels */
     uint32_t last_scr_width, last_scr_height; /* in pixels */
     uint32_t last_depth; /* in bits */
-    uint8_t full_update;
     uint8_t cursor_start, cursor_end;
     uint32_t cursor_offset;
     unsigned int (*rgb_to_pixel)(unsigned int r,