efi_loader: split off detaching SetVirtualAddress()

The runtime services SetVirtualAddress() and ConvertPointer() become
unavailable after SetVirtualAddress(). Other runtime services become
unavailable after ExitBootServices.

Move the update of SetVirtualAddress() and ConvertPointer() to
efi_relocate_runtime_table().

Use functions with the correct signature when detaching.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>