[boot] Set up CR4 in bootloader

Moving the initial CR4 settings from the kernel's `memory_initialize`
(where it doesn't really fit anyway) to the bootloader's `hardware.cpp`.

src/boot/hardware.cpp

@@ -36,6 +36,19 @@ find_acpi_table(uefi::system_table *st)
 	return reinterpret_cast<void*>(acpi1_table);
 }
 
+void
+setup_cr4()
+{
+	uint64_t cr4 = 0;
+	asm volatile ( "mov %%cr4, %0" : "=r" (cr4) );
+	cr4 |=
+		0x000080 | // Enable global pages
+		0x000200 | // Enable FXSAVE/FXRSTOR
+		0x010000 | // Enable FSGSBASE
+		0x020000 | // Enable PCIDs
+		0;
+	asm volatile ( "mov %0, %%cr4" :: "r" (cr4) );
+}
 
 } // namespace hw
 } // namespace boot