xy_setup_blt: Add missing space check
xy_text_immediate: Fix space checking
xy_setup_blt: Fix offset
batch: Add reserved commands

These are MI_BATCH_BUFFER_END, and potentially MI_NOOP to get
quadword-aligned.
batch: Use intel_batch_check_space instead of doing comparison ourselves
blt: Make XY_TEXT_BLT and XY_TEXT_IMMEDIATE_BLT return error instead of submitting batch buffer

This allows the user to send an additional XY_SETUP_BLT in this case.