[riscv] Avoid potentially overwriting the scratch area during relocation

We do not currently describe the temporary page table or the temporary
stack as areas to be avoided during relocation of the iPXE image to a
new physical address.

Perform the copy of the iPXE image and zeroing of the .bss within
libprefix.S, after we have no futher use for the temporary page table
or the temporary initial stack.  Perform the copy and registration of
the system device tree in C code after relocation is complete and the
new stack (within .bss) has been set up.

This provides a clean separation of responsibilities between the
RISC-V libprefix.S and the architecture-independent fdtmem.c.  The
prefix is responsible only for relocating iPXE to the new physical
address returned from fdtmem_relocate(), and doesn't need to know or
care where fdtmem.c is planning to place the copy of the device tree.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/riscv/prefix/libprefix.S

@@ -1023,6 +1023,21 @@ install:
 	la	s6, _prefix
 	sub	s6, s5, s6
 
+	/* Copy iPXE image to new location and zero .bss */
+	mv	t0, s5
+	la	t1, _prefix
+	la	t2, _edata
+1:	LOADN	t3, (t1)
+	STOREN	t3, (t0)
+	addi	t0, t0, ( __riscv_xlen / 8 )
+	addi	t1, t1, ( __riscv_xlen / 8 )
+	blt	t1, t2, 1b
+	la	t1, _ebss
+	add	t1, t1, s6
+2:	STOREN	zero, (t0)
+	addi	t0, t0, ( __riscv_xlen / 8 )
+	blt	t0, t1, 2b
+
 	/* Jump to relocated copy */
 	la	t0, 1f
 	add	t0, t0, s6
@@ -1042,11 +1057,9 @@ install:
 	/* Store boot hart */
 	STOREN	s0, boot_hart, t0
 
-	/* Register copy of device tree as system device tree */
-	la	a0, sysfdt
-	la	a1, _end
-	li	a2, -1
-	call	fdt_parse
+	/* Copy and register system device tree */
+	phys_to_virt a0, s1
+	call	fdtmem_register
 
 	/* Return to a virtual address in the relocated copy */
 	add	ra, s2, s6