pinctrl: renesas: r8a77990: JTAG pins do not have pull-down capabilities

Hence remove the SH_PFC_PIN_CFG_PULL_DOWN flags from their pin
descriptions.

Fixes: 83f6941a ("pinctrl: sh-pfc: r8a77990: Add bias pinconf support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/da4b2d69955840a506412f1e8099607a0da97ecc.1619785375.git.geert+renesas@glider.be