arm64: dts: st: fix timer used for ticks

Remove always-on on generic ARM timer as the clock source provided by
STGEN is deactivated in low power mode, STOP1 by example.

Fixes: 5d30d03a ("arm64: dts: st: introduce stm32mp25 SoCs family")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20250515151238.1.I85271ddb811a7cf73532fec90de7281cb24ce260@changeid


Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>