Fix Registry Isolation issues with Server 2025

Fix Registry Isolation issues with Server 2025

Use MmGetSystemRoutineAddress to dynamically get IoOpenDriverRegistryKey,
which is not present on Server 2016.
Where possible, use IoOpenDriverRegistryKey to avoid opening absolute registry
paths, which is a driver verifier violation on Server 2025 WHQL testing.

Also refactors all registry access to use functions in registry.h and cleans up
driver.c to be more inline with other drivers.

Signed-off-by: Owen Smith <owen.smith@cloud.com>