package/pixman: only compile with riscv vector support when selected

Pixman defaults to building with the riscv vector extension. Instead,
only build with vector if the buildroot user has selected
BR2_RISCV_ISA_RVV.

This option exists since pixman 0.44.0, to which the Buildroot package
was updated as part of Buildroot commit
ba2fb599cd002b57fa70e978d91884c98d8aad05.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/pixman/pixman.mk

@@ -74,6 +74,12 @@ else
 PIXMAN_CONF_OPTS += -Da64-neon=disabled
 endif
 
+ifeq ($(BR2_RISCV_ISA_RVV),y)
+PIXMAN_CONF_OPTS += -Drvv=enabled
+else
+PIXMAN_CONF_OPTS += -Drvv=disabled
+endif
+
 PIXMAN_CFLAGS = $(TARGET_CFLAGS)
 
 ifeq ($(BR2_TOOLCHAIN_HAS_GCC_BUG_101737),y)