The pxa2xx palette entry "16bpp plus transparency" format is
xxxxxxxTRRRRR000GGGGGG00BBBBB000, and "18bpp plus transparency" is
xxxxxxxTRRRRRR00GGGGGG00BBBBBB00.

Correct errors in the code for reading these and converting
them to the internal format. In particular, the buggy code
was attempting to mask out bit 24 of a uint16_t, which
Coverity spotted as an error.
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1400233901-31785-1-git-send-email-peter.maydell@linaro.org