drm/xe/oa: Allow oa_exponent value of 0

drm/xe/oa: Allow oa_exponent value of 0

OA exponent value of 0 is a valid value for periodic reports. Allow user
to pass 0 for the OA sampling interval since it gets converted to 2 gt
clock ticks.

v2: Update the check in xe_oa_stream_init as well (Ashutosh)
v3: Fix mi-rpc failure by setting default exponent to -1 (CI)
v4: Add the Fixes tag

Fixes: b6fd51c62119 ("drm/xe/oa/uapi: Define and parse OA stream properties")
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/20250221213352.1712932-1-umesh.nerlige.ramappa@intel.com