Enable enumeration of writeback connectors if both libdrm and the device
support it. The new Card::has_writeback() method report if the card
support writeback connectors.

Existing code that expect all connectors to model an output may be
confused by the sudden availability of new connectors. To handle this
issue,

- add a KMSXX_DISABLE_WRITEBACK_CONNECTORS environment variable to
  disable enumeration of writeback connectors, similarly to universal
  planes ; and

- ignore writeback connectors where no specific connector is requested
  (Card::get_first_connected_connector(),
  ResourceManager::reserve_connector() if no connector name is
  specified, and applications that use all connected outputs).

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

We can use std::format() and a custom print() wrapper with C++20. When
moving to C++23, we can drop the wrapper.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

Fix cppcheck shadowVariable and shadowArgument warnings by renaming
local variables to avoid conflicts:
- Rename 'ob' to 'prop' in property creation loop in card.cpp
- Rename loop variable 'y_offset' to 'y_off' in conv-yuv-semiplanar.h
- Rename local 'y' to 'y_val' in SMPTE pattern generator in testpat.cpp
- Rename 'is_last' to 'child_is_last' in entry printing in kmsprint.cpp

These changes eliminate naming conflicts while preserving functionality
and improving code clarity.

Fix cppcheck performance warnings by passing function parameters
by const reference instead of by value, preventing unnecessary
copies:
- string parameters in open_device_by_path()
- set<Connector*> parameters in connector finder functions
- vector parameter in FlipState constructor
- range variable in kmscapture loop

These changes improve performance by avoiding object copies while
maintaining the same functionality.

C-style casts should be replaced with appropriate C++ cast operators
for better type safety and code clarity. This change fixes cppcheck
style warnings about C-style pointer casting by using:
- static_cast for simple pointer type conversions
- reinterpret_cast for memory buffer pointer arithmetic

The changes maintain identical functionality while following modern
C++ best practices for explicit casting.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>