dvrmisc: add support for CFW devctls

[pcm720]

This PR adds support for DVRPwned devctls to the dvrmisc module:

• 0x5690 - CFW ping command
• 0x5691 - Get the total number of sectors for the device
• 0x5692 - Memory peek/poke functionality

Tested on PSX DESR-7100 with DVRPwned 2.0.0:

  Devctl test:
  DVRMISC_DEVCTL_CFW_PING: cmd res 0
  DVRMISC_DEVCTL_CFW_GET_MAX_LBA48 for device 0: cmd res 0, result: 0x1dcd8000
  DVRMISC_DEVCTL_CFW_GET_MAX_LBA48 for device 1: cmd res -19, result: 0x0
  DVRMISC_DEVCTL_CFW_GET_MAX_LBA48 for device 2: cmd res -22, result: 0x0
  8-bit mem peek @ 0x1003216e:
                cmd res 0; old value: 0x00000080, cur value: 0x00000080
  8-bit mem poke @ 0x1003216e with 0x000000aa and mask 0x000000ff:
                cmd res 0; old value: 0x00000080, cur value: 0x000000aa
  8-bit mem poke @ 0x1003216e with 0x000000bb and mask 0x0000000f:
                cmd res 0; old value: 0x000000aa, cur value: 0x000000ab
  16-bit mem peek @ 0x10031ef0:
                cmd res 0; old value: 0x00000520, cur value: 0x00000520
  16-bit mem poke @ 0x10031ef0 with 0x0000dead and mask 0x0000ffff:
                cmd res 0; old value: 0x00000520, cur value: 0x0000dead
  16-bit mem poke @ 0x10031ef0 with 0x0000f2ff and mask 0x0000ff00:
                cmd res 0; old value: 0x0000dead, cur value: 0x0000f2ad
  32-bit mem peek @ 0x10031ef4:
                cmd res 0; old value: 0x1002859c, cur value: 0x1002859c
  32-bit mem poke @ 0x10031ef4 with 0x2200f2ff and mask 0xffffffff:
                cmd res 0; old value: 0x1002859c, cur value: 0x2200f2ff
  32-bit mem poke @ 0x10031ef4 with 0x1002859c and mask 0xff00ffff:
                cmd res 0; old value: 0x2200f2ff, cur value: 0x1000859c

[uyjulian]

Lgtm