hikey960: fix build issue for clang

plat/hisilicon/hikey960/include/plat_macros.S:19:55: error: unexpected token in
'.asciz' directive
 .asciz "gicd_ispendr regs (Offsets 0x200 - 0x278)\n" " Offset:\t\t\tvalue\n"
                                                      ^
Makefile:720: recipe for target 'build/hikey960/debug/bl1/cortex_a53.o' failed
make: *** [build/hikey960/debug/bl1/cortex_a53.o] Error 1

Merge the two lines into one.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>