[sw] cleanup and update software framework

[stnolting]

• ⚠️ deprecate IRQ enable/disable functions (wrappers are added to maintain backwards compatibility):
  • void neorv32_cpu_eint(void)
  • void neorv32_cpu_dint(void)
  • int neorv32_cpu_irq_enable(uint8_t irq_sel)
  • int neorv32_cpu_irq_disable(uint8_t irq_sel)
• add new functions for CSR access:
  • void neorv32_cpu_csr_set(const int csr_id, uint32_t mask)
  • void neorv32_cpu_csr_clr(const int csr_id, uint32_t mask)
• rework CPU busy-wait function void neorv32_cpu_delay_ms(uint32_t time_ms)
• 🐛 fixed bug in constructor calling in crt0
• update example programs fixing several minor issues
• minor bootloader edits
• update pre-compiled application images