drm/amdgpu: use DISCOVERY_TMR_SIZE in ACPI TMR fallback

drm/amdgpu: use DISCOVERY_TMR_SIZE in ACPI TMR fallback

amdgpu_acpi_get_tmr_info() returns the full TMR region size, not the IP
discovery table size. Using tmr_size as discovery.size can lead to oversized
allocations and probe failure.

In the ACPI fallback path, keep discovery.size as DISCOVERY_TMR_SIZE and only
use ACPI data for offset calculation.

Fixes: 01bdc7e219c4 ("drm/amdgpu: New interface to get IP discovery binary v3")
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>