All the more recent vendor files have them, so include them for samr30 too.
It is expected for this to become obsolete with the next vendor file update.
samr30 is the only MCU of this family where the vendor files do not
define the PIN_($pin)_EIC_EXTINT_NUM macro yet.
This macro is needed to create a generic EXTI configuration for all
sam0 MCUs.
The defines were generated with
sed -Ei '/define PIN_(.*)_EIC_EXTINT([0-9]*)/
{h; x;
s/define PIN_(.*)A_EIC_EXTINT([0-9]*)(.*)/
define PIN_\1A_EIC_EXTINT_NUM _L_\(\2\)
\/**< \brief EIC signal: PIN_\1 External Interrupt Line *\/
/g; G}' samr30g18a.h samr30e18a.h
