drm/ast: Use constants for SCU registers

drm/ast: Use constants for SCU registers

SCU is the System Control Unit. SCU registers are located in the memory
range at [0x1e6e2000, 0x1e6e2fff]. Refer to them with constants named
AST_REG_SCU<n>, where <n> is the byte offset into the range.

Replacing the magic values in the ast driver was done with grep and sed
as shown below

  git grep -l \,\ 0x1e6e2 | xargs sed -i -e 's/, 0x1e6e2/, AST_REG_SCU/g'
  git grep -l \,\ 0x1E6E2 | xargs sed -i -e 's/, 0x1E6E2/, AST_REG_SCU/g'

plus some manual fixes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patch.msgid.link/20260327133532.79696-6-tzimmermann@suse.de