boards: st: stm32l562e_dk: correct ns variant RAM info

TF-M owns the last 64kByte of SoC internal SRAM1 in 'ns' variant of
board stm32l562e_dk. Update the board variant DTS and YAML files
accordingly and remove the default allocation of 2kB of malloc pool
that worked around this missing information.

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
3 files changed