bcm27xx: remove linux 4.19 support

target/linux/bcm27xx/bcm2708/config-4.19

target/linux/bcm27xx/bcm2709/config-4.19

target/linux/bcm27xx/bcm2710/config-4.19

target/linux/bcm27xx/bcm2711/config-4.19

...rm-partially-revert-702b94bff3c50542a6e4ab9a4f4cef0.patch

...-4.19/950-0002-smsx95xx-fix-crimes-against-truesize.patch

...msc95xx-Experimental-Enable-turbo_mode-and-packetsi.patch

...19/950-0004-Allow-mac-address-to-be-set-in-smsc95xx.patch

...rotect-__release_resource-against-resources-without.patch

...rq-bcm2836-Prevent-spurious-interrupts-and-trap-the.patch

.../950-0007-irq-bcm2836-Avoid-Invalid-trigger-warning.patch

...tches-4.19/950-0008-irqchip-bcm2835-Add-FIQ-support.patch

...9/950-0009-irqchip-irq-bcm2835-Add-2836-FIQ-support.patch

...0010-spi-bcm2835-Support-pin-groups-other-than-7-11.patch

....19/950-0011-spi-bcm2835-Disable-forced-software-CS.patch

...atches-4.19/950-0012-spi-bcm2835-Remove-unused-code.patch

...maengine-bcm2835-Load-driver-early-and-support-lega.patch

...tches-4.19/950-0014-firmware-Updated-mailbox-header.patch

...-4.19/950-0015-rtc-Add-SPI-alias-for-pcf2123-driver.patch

...6-watchdog-bcm2835-Support-setting-reboot-partition.patch