LcdGraphicsOutputDxe: Update FrameBufferSize as per UEFI spec section 11.9

The shift by 1 on the left was expected. It eases the access to CSSELR and set/way operations
where the cache level field is at the BIT1 position.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14705 6f19259b-4bc3-4df7-8a09-765794883524