BTT EXP-MOT with MKS Robin E3D

I wanted to add 1 additional stepper driver to my MKS ROBIN E3D so that I can do Z_TILT.

E3D UART mode
MOT-EXP UART mode
E3D EXP1 <-> EXP-MOT EXP1
E3D EXP2 <-> EXP-MOT EXP2

Following the [BTT EXP-MOT user guide](https://github.com/bigtreetech/BTT-Expansion-module/blob/master/BTT%20EXP-MOT/BTT%20EXP-MOT%20V1.0User%20Guide.pdf) and cross referencing with the [E3D pins](https://github.com/makerbase-mks/MKS-Robin-E3-E3D/blob/master/hardware/MKS%20Robin%20E3D%20V1.1_003/MKS%20Robin%20E3D%20V1.1_003%20PIN.pdf)

BTT-MOT EXP2 M1STP = E3D EXP2 PB15 (klipper alias EXP2_6)
BTT-MOT EXP2 M1DIR = E3D EXP2 PB0 (klipper alias EXP2_5)
BTT-MOT EXP2 M1EN = E3D EXP2 PC10 (klipper alias EXP2_7)
BTT-MOT EXP1 M1RX = E3D EXP1 PA7 (klipper alias EXP1_6)

```
[stepper_z1]
step_pin: EXP2_6
dir_pin: !EXP2_5
enable_pin: !EXP2_7
microsteps: 16
rotation_distance: 8
endstop_pin: ^PC6
endstop_pin: probe:z_virtual_endstop

[tmc2209 stepper_z1]
uart_pin: EXP1_6
run_current: 0.8
stealthchop_threshold: 999999

[board_pins]
aliases:
# EXP1 header
EXP1_1=PC1, EXP1_3=PA4, EXP1_5=PA6, EXP1_7=PC4, EXP1_9=,
EXP1_2=PC3, EXP1_4=PA5, EXP1_6=PA7, EXP1_8=PC5, EXP1_10=<5V>,
# EXP2 header
EXP2_1=PB14, EXP2_3=PB11, EXP2_5=PB0, EXP2_7=PC10, EXP2_9=,
EXP2_2=PB13, EXP2_4=PA15, EXP2_6=PB15, EXP2_8=, EXP2_10=,
# CR_EXP3 header - additional header dedicated to Creality Ender 3/5 stock screens
CR_EXP3_10=<5V>, CR_EXP3_8=PA4, CR_EXP3_6=PA6, CR_EXP3_4=, CR_EXP3_2=PC3,
CR_EXP3_9=, CR_EXP3_7=PA5, CR_EXP3_5=PB0, CR_EXP3_3=PB11, CR_EXP3_1=PC1
```

`FORCE_MOVE STEPPER=stepper_z1 DISTANCE=10 VELOCITY=5`

Start by comparing the BTT EXP-MOT user guide with the MKS Robin E3D pin PDF and the supplied Klipper configuration, especially the EXP1 and EXP2 aliases. Reproduce the reported behavior with FORCE_MOVE STEPPER=stepper_z1 DISTANCE=10 VELOCITY=5 and verify whether the additional driver can control Z1 and support Z_TILT; the issue does not name a repository file or provide a textual error.

Written by the indexing model from the issue text.