bootstd: add IGNORE_BOOTABLE option

Qualcomm devices have a ridiculous number of partitions (up in the
triple digits on modern devices) and often have random partitions with
the bootable flag set. However, there is usually not a dedicated ESP
partition, instead some partition has to be repurposed. To support this
usecase, add a new CONFIG_IGNORE_BOOTABLE option which disables the
optimisation added in f0e358f07d75 ("bootstd: Only scan bootable
partitions) and always scans all partitions.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
diff --git a/boot/Kconfig b/boot/Kconfig
index fbc49c5..850a9dc 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -452,6 +452,14 @@
 	  standard boot does not support all of the features of distro boot
 	  yet.
 
+config BOOTSTD_IGNORE_BOOTABLE
+	bool "Don't rely on the bootable flag when scanning bootflows"
+	help
+	  Enable this to avoid relying on the bootable partition flag. On some
+	  devices with complicated partition tables this flag may be set by mistake
+	  resulting in bootflows not being recognised. Set this to always scan all
+	  partitions.
+
 config BOOTMETH_GLOBAL
 	bool
 	help