engine: Add barrier CSR, fix cluster peripherals

[paulsc96]

This MR:

• Integrates the new CSR-based cluster barrier in Banshee (Fast cluster HW barrier snitch_cluster#43)
• Fixes peripheral accesses: They did not properly respect the offset field, making e.g. zero memory accesses report out-of-map errors.

Note that the CSR address is currently hacked into riscv.rs manually, but the resulting generated file should be identical once pulp-platform/riscv-opcodes#9 is merged.