boards: b_u585i_iot02a_ns: Update flash partition w/ upgrade to TF-M V1.7.0

Secure/Non secure partition for target b_u585i_iot02a has been
updated in TF-M v1.7.0, giving more space to bl2 and TF-M.
As a consequence, non secure partition is shifted.

Align fully b_u585i_iot02a_ns flash partition to TF-M partition.
Note that proposed mcuboot partition encompasses following sections in
TF-M flash layout:
- SCRATCH (64KB)
- BL2 - MCUBoot (88KB)
- BL2 - NOHDP (4KB)
- OTP Write Protect (4KB)
- NV counters area (16KB)
- Secure Storage Area (16KB)
- Internal Trusted Storage Area (32KB)

Additionally describe secondary partitions that could be used for
secondary images storage.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>