pds_core: fix cmd_regs access racing BAR unmap on reset

Summary

In the Linux kernel, the following vulnerability has been resolved: pds_core: fix cmd_regs access racing BAR unmap on reset pdsc_reset_prepare() and pdsc_reset_done()'s pdsc_map_bars() error path clear/iounmap cmd_regs without devcmd_lock, and pdsc_legacy_firmware_update()'s download loop derefs cmd_regs after dropping and retaking the lock without re-checking. An FLR concurrent with a devlink flash can unmap cmd_regs under an in-flight devcmd, causing a NULL deref or a write to unmapped MMIO. Take devcmd_lock across the BAR unmap/remap, and re-check cmd_regs in the download loop. Only the PF maps cmd_regs and runs devcmd, so skip the unmap on a VF, as pdsc_remove() and pdsc_reset_done() already do. A reset that completes entirely within the unlocked window is not a correctness problem for the image: the device clears its update session, so a resumed download is rejected, and it verifies the staged image before writing a flash slot, reporting PDS_RC_BAD_FW rather than activating it. pdsc_unmap_bars() also clears info_regs, intr_status and intr_ctrl. The interrupt and start/stop readers of those are quiesced before the unmap by pdsc_fw_down(), which frees the interrupts and tears down the queues. The debugfs readers are not, since those files outlive a reset; that is pre-existing and out of scope here.