ARM: dts: stm32: use uniform node names for sleep pinctrl groups

While all sleep pinctrl group labels now follow a fixed naming scheme,
node _names_ for these groups don't:

- Some use ${dev}-[0-9], where the suffix is the normal group suffix + 1
- Some use ${dev}-sleep-[0-9], where suffix is the normal group suffix
- The &ltdc node uses ${dev}-[a-z]-[0-9], where the letter matches the
  phandle and the number suffix is the normal group's suffix + 1

For uniformity, standardize on using ${dev}-[0-9]+ for all normal
pinctrl groups and ${dev}-sleep-[0-9]+ for all sleep pinctrl groups.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>