Add IDE/ATA disk driver with devicefs integration

Implement PIO-mode IDE driver that scans primary and secondary channels
for ATA hard drives and ATAPI CD/DVD drives using IDENTIFY commands.

Features:
- Scans 4 possible devices (2 channels x 2 drives each)
- ATA IDENTIFY DEVICE for hard drives
- ATAPI IDENTIFY PACKET DEVICE for CD/DVD drives
- PIO-mode 28-bit LBA sector read/write for ATA drives
- Model string extraction and sector count parsing
- Registers as kernel driver via REGISTER_DRIVER macro
- Registers devices with devicefs: ATA → hdd class, ATAPI → cd class
- Added inw/outw to port_io.h for 16-bit I/O

Tested: QEMU detects hdd1 (QEMU HARDDISK) and cd1 (QEMU DVD-ROM).

src/port_io.h

@@ -15,6 +15,18 @@ static inline uint8_t inb(uint16_t port)
     return ret;
 }
 
+static inline void outw(uint16_t port, uint16_t val)
+{
+    asm volatile ( "outw %w0, %w1" : : "a"(val), "Nd"(port) );
+}
+
+static inline uint16_t inw(uint16_t port)
+{
+    uint16_t ret;
+    asm volatile ( "inw %w1, %w0" : "=a"(ret) : "Nd"(port) );
+    return ret;
+}
+
 static inline void io_wait(void)
 {
     /* Port 0x80 is used for 'checkpoints' during POST. */