riscv64/Makefile: disable gp relaxations #1960

Job	Run time
call-ci / build (armv7a7-imx6ull-evk)	1m 7s
call-ci / build (armv7a9-zynq7000-qemu)	1m 17s
call-ci / build (armv7a9-zynq7000-zedboard)	1m 9s
call-ci / build (armv7a9-zynq7000-zturn)	56s
call-ci / build (armv7m4-stm32l4x6-nucleo)	1m 3s
call-ci / build (armv7m7-imxrt105x-evk)	1m 9s
call-ci / build (armv7m7-imxrt106x-evk)	1m 12s
call-ci / build (armv7m7-imxrt117x-evk)	1m 12s
call-ci / build (host-generic-pc)	48s
call-ci / build (ia32-generic-pc)	57s
call-ci / build (ia32-generic-qemu)	1m 2s
call-ci / build (riscv64-generic-qemu)	56s
call-ci / build (riscv64-generic-spike)	1m 6s
call-ci / build (sparcv8leon3-gr716-mini)	1m 5s
call-ci / test HW (armv7a7-imx6ull-evk)	6m 10s
call-ci / test EMU (armv7a9-zynq7000-qemu)	8m 21s
call-ci / test HW (armv7m7-imxrt106x-evk)	2m 37s
call-ci / test EMU (host-generic-pc)	1m 3s
call-ci / test HW (armv7m7-imxrt117x-evk)	2m 57s
call-ci / test EMU (ia32-generic-qemu)	6m 33s
call-ci / test HW (armv7a9-zynq7000-zedboard)	6m 52s
call-ci / test EMU (riscv64-generic-qemu)	5m 20s
call-ci / test HW (armv7m4-stm32l4x6-nucleo)	11m 47s
call-ci / tests-summary	16s
call-ci / send-notification	0s
	1h 6m 55s

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