drm/vkms: change the max cursor width/height

This change expands the coverage for the IGT kms_cursor_crc test, where
the size varies between 64 and 512 for a square cursor. With this, in
addition to the cursor 64x64, this patch enables the test of cursors with
sizes: 128x128, 256x256, and 512x512.

Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200710160313.xjoz6ereyma5vkc3@smtp.gmail.com