ec_commands: Force enum to be at least 16 bits
ec_commands: Force enum to be at least 16 bits

If the values in the enum can fit in a byte, the compiler can optimize
the size of the enum to a byte. However, our protocol requires 16 bits,
so define a max enum value that forces at least 16 bits.

BRANCH=none
BUG=b:144056522
TEST=make buildall -j

Change-Id: I119d990f2775d8b970ec0ec15df1e451fc5dc45d
Signed-off-by: Tom Hughes <fc5c12f30a5ed2baa0581f44ee14ad1eb7b20d83@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1902679
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Commit-Queue: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec