arch: arm64: recalculate panel dimensions (just divided with 10 and rouded)

Plug in 2560x1600 screen size as 10.95 for diagonal at https://www.sven.de/dpi/

Display size: 9.29" × 5.8" = 53.89in² (23.59cm × 14.74cm = 347.67cm²) at 275.7 PPI, 0.0921mm dot pitch, 76008 PPI²

23.59cm  = 236mm (rouded to nearest ceil)
14.74cm  = 147mm

why: https://github.com/dev-harsh1998/android_kernel_xiaomi_nabu/blob/arrow-13.0/Documentation/devicetree/bindings/drm/msm/mdss-dsi-panel.txt#L311


the units should be in mm.

Signed-off-by: Harshit Jain <reach@harsh1998.dev>