Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

include/mp.h

@@ -0,0 +1,54 @@
+// See MultiProcessor Specification Version 1.[14]
+
+struct mp {             // floating pointer
+  uchar signature[4];           // "_MP_"
+  uint32 physaddr;               // 32-bit phys addr of MP config table
+  uchar length;                 // 1
+  uchar specrev;                // [14]
+  uchar checksum;               // all bytes must add up to 0
+  uchar type;                   // MP system config type
+  uchar imcrp;
+  uchar reserved[3];
+};
+
+struct mpconf {         // configuration table header
+  uchar signature[4];           // "PCMP"
+  ushort length;                // total table length
+  uchar version;                // [14]
+  uchar checksum;               // all bytes must add up to 0
+  uchar product[20];            // product id
+  uint32 oemtable_p;               // OEM table pointer
+  ushort oemlength;             // OEM table length
+  ushort entry;                 // entry count
+  uint32 lapicaddr_p;              // address of local APIC
+  ushort xlength;               // extended table length
+  uchar xchecksum;              // extended table checksum
+  uchar reserved;
+};
+
+struct mpproc {         // processor table entry
+  uchar type;                   // entry type (0)
+  uchar apicid;                 // local APIC id
+  uchar version;                // local APIC verison
+  uchar flags;                  // CPU flags
+    #define MPBOOT 0x02           // This proc is the bootstrap processor.
+  uchar signature[4];           // CPU signature
+  uint feature;                 // feature flags from CPUID instruction
+  uchar reserved[8];
+};
+
+struct mpioapic {       // I/O APIC table entry
+  uchar type;                   // entry type (2)
+  uchar apicno;                 // I/O APIC id
+  uchar version;                // I/O APIC version
+  uchar flags;                  // I/O APIC flags
+  uint32 addr_p;                  // I/O APIC address
+};
+
+// Table entry types
+#define MPPROC    0x00  // One per processor
+#define MPBUS     0x01  // One per bus
+#define MPIOAPIC  0x02  // One per I/O APIC
+#define MPIOINTR  0x03  // One per bus interrupt source
+#define MPLINTR   0x04  // One per system interrupt source
+