AtomBIOS ROM should be read-only in userspace

[kallisti5]

While we *should* be using the AtomBIOS video ROM read-only in userspace (aka the accelerant), it causes AtomBIOS to crash on the first execution (populating gpio pins).

radeon_hd: gpio_i2c_populate: i2c GPIO @ 11, valid: true, hwPin: 0x93
radeon_hd: gpio_i2c_populate: i2c GPIO @ 12, valid: true, hwPin: 0x94
radeon_hd: gpio_i2c_populate: i2c GPIO @ 13, valid: true, hwPin: 0x95
radeon_hd: gpio_i2c_populate: i2c GPIO @ 14, valid: true, hwPin: 0x96
debug_server: Thread 96 entered the debugger: Segment violation
stack trace, current PC 0x158b8af5bc  </boot/system/add-ons/accelerants/radeon_hd.accelerant> _Z13gpio_populatev + 0x416:
  (0x3ccecb28c0)  0x158b8ac62a  </boot/system/add-ons/accelerants/radeon_hd.accelerant> radeon_init_accelerant + 0x1de
  (0x3ccecb2910)  0x31c298b1de  </boot/system/servers/app_server> _ZN21AccelerantHWInterface15_OpenAccelerantEi + 0x10c
  (0x3ccecb2e30)  0x31c298b2ee  </boot/system/servers/app_server> _ZN21AccelerantHWInterface10InitializeEv + 0x56
  (0x3ccecb2e60)  0x31c2953aa0  </boot/system/servers/app_server> _ZN13ScreenManager15_AddHWInterfaceEP11HWInterface + 0x46
  (0x3ccecb2eb0)  0x31c2953d64  </boot/system/servers/app_server> _ZN13ScreenManagerC1Ev + 0x50
  (0x3ccecb2f30)  0x31c293d6e8  </boot/system/servers/app_server> _ZN9AppServerC2EPi + 0xca
  (0x3ccecb2f70)  0x31c293c926  </boot/system/servers/app_server> main + 0x26
  (0x3ccecb2fa0)  0x31c293cc6e  </boot/system/servers/app_server> _start + 0x3a
  (0x3ccecb2fd0)  0x294eea610e  </boot/system/runtime_loader> runtime_loader + 0xd4
consoled: error -2 starting console.

To ensure the radeon_hd driver continues to function after ​https://cgit.haiku-os.org/haiku/commit/?id=16e17faf59ed62b1e4469fb5c6e46791033c3179, we have made it R/W for now.

We need to investigate why AtomBIOS wants the video rom R/W