Add support for `rp235_arm_ns` binaries

[kilograham]

• These are non-secure binaries that are launched by a secure counterpart
• These are independent SDK binaries linked in their own right
• They should be linked to run at 0x10400000 or 0x10800000 or 0x10c00000
• There needs to be support for launching the NS binary from S code
• The NS binary must only initialize h/w it owns
• The secure side of the SDK must provide helper functions such as "launch NS code on core 1"
• The secure side of the SDK should provide other secure helper functionality required to implement any pertinent SDK features on the NS side, and provide them via the bootrom secure_call mechanism

A good test case would be running Micropython under some secure firmware