RP2350 TRNG support

[ionspin]

This is a driver for RP2350 TRNG, I used RNG driver from embassy-nrf as a template, but adapted to be more in line with other drivers in embassy-rp.

From 2350 datasheet:

12.12.1. Overview
RP2350 contains an Arm IP-based True Random Number Generator block. It supports the following features:
• Compliance with FIPS Publication 140-2, BSI AIS-31, and NIST SP 800-90B
• Produces approximately 7.5 kb/s of entropy when the core runs at 150 MHz
On request, the TRNG block generates a block of 192 entropy bits generated by automatically processing a series of
periodic samples from the TRNG block’s internal Ring Oscillator (ROSC).

The TRNG block’s ROSC is a free-running oscillator with no direct connection to the system clocks on RP2350. As a
result, the ROSC generally runs asynchronously to the system clocks.
After a sufficient number of samples have been collected, the TRNG block completes the generation process and
presents the random number in the EHR_DATA[x] result registers.

They go on to note that Pico SDK and Pico Bootrom disable all entropy checks and sample as fast as possible from the TRNG ROSC directly, and then pass the data through SHA256 before using it (hardware accelerated in case of Bootrom) or xiroshiro128** (in case of pico-random library in Pico SDK , note that xiroshiro128** is verions 1.0 there) .

I've decided to leave the entropy checks enabled and datasheet recommended config for the TRNG default config as they seem to be sane.

Related to #3241

[Dirbaio]

thanks!