ANDROID: gki_defconfig: Enable RCU_BOOST config

Config helps to boost the priority of preempted RCU readers that
block the current preemptible RCU grace period for too long.
Enable CONFIG_RCU_BOOST for both arm64 and x86 architectures
in android13-5.15 kernel.

Bug: 234812192
Change-Id: I97225856dc696382cc78dd1520632d47da3f5f76
Signed-off-by: Prasad Sodagudi <quic_psodagud@quicinc.com>