defconfig: sa415m and sa415m-perf: Disable bluetooth builtin

1. Configure CONFIG_BT=n for bluetooth-power DLKM.
2. Configure CONFIG_SLIMBUS=y as it needs to use slimbus
   interface. Why it doesn't need to add this before? Because
   before CONFIG_BT=y, then CONFIG_BTFM_SLIM will be y, which
   will set CONFIG_SLIMBUS to y.

CRs-Fixed: 2547124
Change-Id: I6513a18470358d07417e6a124300c0f14674f794
Signed-off-by: Junlin Zhang <junlzhan@codeaurora.org>