Use serial for output without LFB

[IanSeyler]

This pull request adds support for serial port interrupts and improves the integration of serial input/output with the system's input handling. The main changes include configuring the serial interrupt handler, updating the input and output routines to handle both keyboard and serial input, and ensuring proper processing of special characters in serial output.

Serial port interrupt support:

• Added configuration for the serial interrupt handler in serial_init: to set up the interrupt gate, enable the serial IRQ, and configure the serial port to generate interrupts when data is available. (src/drivers/serial.asm)
• Implemented the int_serial: interrupt handler, which calls the serial input routine, acknowledges the IRQ, and wakes up all SMP threads as a workaround. (src/interrupt.asm)
• Added the serial_interrupt: routine to receive characters from the serial port and treat them as keyboard input. (src/drivers/serial.asm)

Input/output integration improvements:

• Updated the b_input syscall to scan for input from both keyboard and serial sources, using the shared key variable set by interrupt handlers. (src/syscalls/io.asm)
• Enhanced the serial output routine to handle special characters: backspace (decrement cursor) and line feed (convert to carriage return + line feed), ensuring correct serial output formatting. (src/syscalls/io.asm) [1] [2]