illumos gate

Currently, efi_cons_getchar() will wait for a key. While this seems to make sense, the implementation of getchar()
in common/console.c will loop across getchar() for all consoles without doing ischar() first.

This means that if we've configured multiple consoles such as "ttyb,text", we can't input into
the serial, as getchar() will be sat waiting for input only from efi_console.c

One version of the fix would fix the common routine so it calls into ->c_ready() first for each
console. However, as this is used on legacy BIOS, it seems better to get efi_console.c in line
with the other implementations instead, so any risk of odd behaviour is reduced.

We will also fix the ischar() implementation in efi_console.c so it's properly idempotent.