Bug description:   When the menu is refresh type, and the old string is longer than new string, after refresh, some old string will still show. The mainly change is:   1. This change cleans the old string first and then paints the new string.   2. Fixed old code checks grayout flag not correct.
Bug description:
  When the menu is refresh type, and the old string is longer than new string, after refresh, some old string will still show.
The mainly change is:
  1. This change cleans the old string first and then paints the new string.
  2. Fixed old code checks grayout flag not correct.

git-svn-id: 5648d1bec6962b0a6d1d1b40eba8cf5cdb62da3d@11354 6f19259b-4bc3-4df7-8a09-765794883524

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2