Kernel: Set up an initial boot framebuffer console

Instead of seeing a black screen until GraphicsManagement was fully
initialized, this allows us to see the console output much earlier.
So, if the bootloader provided us with a framebuffer, set up a console
as early as possible.

Kernel/Graphics/Console/BootFramebufferConsole.cpp

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Graphics/Console/BootFramebufferConsole.h>
+#include <Kernel/Locking/Spinlock.h>
+#include <Kernel/Memory/MemoryManager.h>
+
+namespace Kernel::Graphics {
+
+BootFramebufferConsole::BootFramebufferConsole(PhysicalAddress framebuffer_addr, size_t width, size_t height, size_t pitch)
+    : GenericFramebufferConsoleImpl(width, height, pitch)
+{
+    // NOTE: We're very early in the boot process, memory allocations shouldn't really fail
+    auto framebuffer_end = Memory::page_round_up(framebuffer_addr.offset(height * pitch * sizeof(u32)).get()).release_value();
+    m_framebuffer = MM.allocate_kernel_region(framebuffer_addr.page_base(), framebuffer_end - framebuffer_addr.page_base().get(), "Boot Framebuffer"sv, Memory::Region::Access::ReadWrite).release_value();
+    [[maybe_unused]] auto result = m_framebuffer->set_write_combine(true);
+    m_framebuffer_data = m_framebuffer->vaddr().offset(framebuffer_addr.offset_in_page()).as_ptr();
+    memset(m_framebuffer_data, 0, height * pitch * sizeof(u32));
+}
+
+void BootFramebufferConsole::clear(size_t x, size_t y, size_t length)
+{
+    SpinlockLocker lock(m_lock);
+    if (m_framebuffer_data)
+        GenericFramebufferConsoleImpl::clear(x, y, length);
+}
+
+void BootFramebufferConsole::clear_glyph(size_t x, size_t y)
+{
+    VERIFY(m_lock.is_locked());
+    GenericFramebufferConsoleImpl::clear_glyph(x, y);
+}
+
+void BootFramebufferConsole::enable()
+{
+    // Once disabled, ignore requests to re-enable
+}
+
+void BootFramebufferConsole::disable()
+{
+    SpinlockLocker lock(m_lock);
+    GenericFramebufferConsoleImpl::disable();
+    m_framebuffer = nullptr;
+    m_framebuffer_data = nullptr;
+}
+
+void BootFramebufferConsole::write(size_t x, size_t y, char ch, Color background, Color foreground, bool critical)
+{
+    SpinlockLocker lock(m_lock);
+    if (m_framebuffer_data)
+        GenericFramebufferConsoleImpl::write(x, y, ch, background, foreground, critical);
+}
+
+u8* BootFramebufferConsole::framebuffer_data()
+{
+    VERIFY(m_lock.is_locked());
+    VERIFY(m_framebuffer_data);
+    return m_framebuffer_data;
+}
+
+}