linux-raspberrypi: Fix defconfig for RPi4-64

emmc dt node uses iproc sdhci driver. Make sure it is enabled.
https://github.com/raspberrypi/linux/pull/3045

Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

recipes-kernel/linux/files/raspberrypi4-64/rpi4-64-kernel-misc.cfg

@@ -0,0 +1,2 @@
+# see emmc node
+CONFIG_MMC_SDHCI_IPROC=y

recipes-kernel/linux/linux-raspberrypi_4.19.bb

@@ -7,6 +7,7 @@ SRCREV = "9d1deec93fa8b1b4953ff5e9210349f3c85b9a8d"
 SRC_URI = " \
     git://github.com/raspberrypi/linux.git;protocol=git;branch=${LINUX_RPI_BRANCH} \
     "
+SRC_URI_append_raspberrypi4-64 = " file://rpi4-64-kernel-misc.cfg"
 require linux-raspberrypi.inc
 
 LIC_FILES_CHKSUM = "file://COPYING;md5=bbea815ee2795b2f4230826c0c6b8814"