drm/xe/oa: Ensure that polled read returns latest data

In polled mode, user calls poll() for read data to be available before
performing a read(). In the duration between these 2 calls, there may be
new data available in the OA buffer. To ensure user reads all available
data, check for latest data in the OA buffer in polled read.

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250212010255.1423343-1-umesh.nerlige.ramappa@intel.com