Fix build in qemu_capabilities

Fix build in qemu_capabilities

Commit f05b6a91 added virQEMUDriverConfigPtr argument to the
virQEMUCapsFillDomainCaps function and it uses forward declaration
of virQEMUDriverConfig and virQEMUDriverConfigPtr that casues clang
build to fail:

gmake[3]: Entering directory `/usr/home/novel/code/libvirt/src'
  CC       qemu/libvirt_driver_qemu_impl_la-qemu_capabilities.lo
In file included from qemu/qemu_capabilities.c:43:
In file included from qemu/qemu_hostdev.h:27:
qemu/qemu_conf.h:63:37: error: redefinition of typedef 'virQEMUDriverConfig'
is a C11 feature [-Werror,-Wtypedef-redefinition]
typedef struct _virQEMUDriverConfig virQEMUDriverConfig;
                                    ^
qemu/qemu_capabilities.h:328:37: note: previous definition is here
typedef struct _virQEMUDriverConfig virQEMUDriverConfig;
                                    ^

Fix that by passing loader and nloader config attributes directly
instead of passing complete config.